diff --git a/.gitignore b/.gitignore
index ee73fd369..ef2407e15 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@ t/servroot*
 lua-resty-mlcache-*/
 *.tar.gz
 *.rock
+work/
diff --git a/.travis.yml b/.travis.yml
index 56c81effb..94549ad85 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,17 +18,18 @@ cache:
 env:
   global:
     - JOBS=2
-    - LUAROCKS=3.2.1
+    - LUAROCKS=3.4.0
     - TEST_NGINX_RANDOMIZE=1
   matrix:
-    - OPENRESTY=1.15.8.2
+    - OPENRESTY=1.19.3.1
+    - OPENRESTY=1.17.8.2
+    - OPENRESTY=1.17.8.1
+    - OPENRESTY=1.15.8.3
     - OPENRESTY=1.15.8.1
     - OPENRESTY=1.13.6.2
     - OPENRESTY=1.13.6.1
     - OPENRESTY=1.11.2.5
-    - OPENRESTY=1.11.2.4
-    - OPENRESTY=1.11.2.3
-    - OPENRESTY=1.11.2.2
+    - OPENRESTY=1.11.2.1
 
 before_install:
   - mkdir -p download-cache
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6dc22fd54..4e9838efe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # Table of Contents
 
+- [2.5.0](#2.5.0)
 - [2.4.1](#2.4.1)
 - [2.4.0](#2.4.0)
 - [2.3.0](#2.3.0)
@@ -12,6 +13,32 @@
 - [1.0.1](#1.0.1)
 - [1.0.0](#1.0.0)
 
+## [2.5.0]
+
+> Released on: 2020/11/18
+
+#### Added
+
+- `get()` callback functions are now optional. Without a callback, `get()` now
+  still performs on-cpu L1/L2 lookups (no yielding). This allows implementing
+  new cache lookup patterns guaranteed to be on-cpu for a more constant,
+  smoother latency tail end (e.g. values are refreshed in background timers with
+  `set()`).
+  Thanks Hamish Forbes and Corina Purcarea for proposing this feature and
+  participating in its development!
+  [#96](https://github.com/thibaultcha/lua-resty-mlcache/pull/96)
+
+#### Fixed
+
+- Improve `update()` robustness to worker crashes. Now, the library behind
+  `cache:update()` is much more robust to re-spawned workers when initialized in
+  the `init_by_lua` phase.
+  [#97](https://github.com/thibaultcha/lua-resty-mlcache/pull/97)
+- Document the `peek()` method `stale` argument which was not mentioned, as well
+  as the possibility of negative TTL return values for expired items.
+
+[Back to TOC](#table-of-contents)
+
 ## [2.4.1]
 
 > Released on: 2020/01/17
@@ -215,6 +242,7 @@ Initial release.
 
 [Back to TOC](#table-of-contents)
 
+[2.5.0]: https://github.com/thibaultcha/lua-resty-mlcache/compare/2.4.1...2.5.0
 [2.4.1]: https://github.com/thibaultcha/lua-resty-mlcache/compare/2.4.0...2.4.1
 [2.4.0]: https://github.com/thibaultcha/lua-resty-mlcache/compare/2.3.0...2.4.0
 [2.3.0]: https://github.com/thibaultcha/lua-resty-mlcache/compare/2.2.1...2.3.0
diff --git a/README.md b/README.md
index e2c6e8b6f..1b49989c6 100644
--- a/README.md
+++ b/README.md
@@ -159,14 +159,11 @@ Tests matrix results:
 | OpenResty   | Compatibility
 |------------:|:--------------------|
 | <           | not tested
-| `1.11.2.2`  | :heavy_check_mark:
-| `1.11.2.3`  | :heavy_check_mark:
-| `1.11.2.4`  | :heavy_check_mark:
-| `1.11.2.5`  | :heavy_check_mark:
-| `1.13.6.1`  | :heavy_check_mark:
-| `1.13.6.2`  | :heavy_check_mark:
-| `1.15.8.1`  | :heavy_check_mark:
-| `1.15.8.2`  | :heavy_check_mark:
+| `1.11.2.x`  | :heavy_check_mark:
+| `1.13.6.x`  | :heavy_check_mark:
+| `1.15.8.x`  | :heavy_check_mark:
+| `1.17.8.x`  | :heavy_check_mark:
+| `1.19.3.x`  | :heavy_check_mark:
 | >           | not tested
 
 [Back to TOC](#table-of-contents)
@@ -333,16 +330,16 @@ Lua VM will be created for every request.
 
 get
 ---
-**syntax:** `value, err, hit_level = cache:get(key, opts?, callback, ...)`
+**syntax:** `value, err, hit_level = cache:get(key, opts?, callback?, ...)`
 
 Perform a cache lookup. This is the primary and most efficient method of this
 module. A typical pattern is to *not* call [set()](#set), and let [get()](#get)
 perform all the work.
 
-When it succeeds, it returns `value` and no error. **Because `nil` values from
-the L3 callback are cached to signify misses, `value` can be nil, hence one
-must rely on the second return value `err` to determine if this method
-succeeded or not**.
+When this method succeeds, it returns `value` and no error. **Because `nil`
+values from the L3 callback can be cached (i.e. "negative caching"), `value` can
+be nil albeit already cached. Hence, one must rely on the second return value
+`err` to determine if this method succeeded or not**.
 
 The third return value is a number which is set if no error was encountered.
 It indicated the level at which the value was fetched: `1` for L1, `2` for L2,
@@ -410,8 +407,8 @@ options:
   tables, cdata objects, loading new Lua code, etc...
   **Default:** inherited from the instance.
 
-The third argument `callback` **must** be a function. Its signature and return
-values are documented in the following example:
+The third argument `callback` is optional. If provided, it must be a function
+whose signature and return values are documented in the following example:
 
 ```lua
 -- arg1, arg2, and arg3 are arguments forwarded to the callback from the
@@ -433,11 +430,29 @@ local function callback(arg1, arg2, arg3)
 end
 ```
 
-This function is allowed to throw Lua errors as it runs in protected mode. Such
-errors thrown from the callback will be returned as strings in the second
-return value `err`.
+The provided `callback` function is allowed to throw Lua errors as it runs in
+protected mode. Such errors thrown from the callback will be returned as strings
+in the second return value `err`.
 
-When called, `get()` follows the below logic:
+If `callback` is not provided, `get()` will still lookup the requested key in
+the L1 and L2 caches and return it if found. In the case when no value is found
+in the cache **and** no callback is provided, `get()` will return `nil, nil,
+-1`, where -1 signifies a **cache miss** (no value). This is not to be confused
+with return values such as `nil, nil, 1`, where 1 signifies a **negative cached
+item** found in L1 (cached `nil`).
+
+```lua
+local value, err, hit_lvl = cache:get("key")
+if value == nil then
+    if hit_lvl == -1 then
+        -- miss (no value)
+    end
+
+    -- negative hit (cached `nil`)
+end
+```
+
+When provided a callback, `get()` follows the below logic:
 
 1. query the L1 cache (lua-resty-lrucache instance). This cache lives in the
    Lua VM, and as such, it is the most efficient one to query.
@@ -465,7 +480,9 @@ When called, `get()` follows the below logic:
    are unlocked and read the value from the L2 cache (they do not run the L3
    callback) and return it.
 
-Example:
+When not provided a callback, `get()` will only execute steps 1. and 2.
+
+Here is a complete example usage:
 
 ```lua
 local mlcache = require "mlcache"
@@ -504,8 +521,8 @@ else
 end
 ```
 
-This second example is a modification of the above one, in which we apply
-some transformation to the retrieved `user` record, and cache it via the
+This second example is similar to the one above, but here we apply some
+transformation to the retrieved `user` record before caching it via the
 `l1_serializer` callback:
 
 ```lua
@@ -701,31 +718,35 @@ end
 
 peek
 ----
-**syntax:** `ttl, err, value = cache:peek(key)`
+**syntax:** `ttl, err, value = cache:peek(key, stale?)`
 
 Peek into the L2 (`lua_shared_dict`) cache.
 
-The first and only argument `key` is a string, and it is the key to lookup.
+The first argument `key` is a string which is the key to lookup in the cache.
+
+The second argument `stale` is optional. If `true`, then `peek()` will consider
+stale values as cached values. If not provided, `peek()` will consider stale
+values, as if they were not in the cache
 
 This method returns `nil` and a string describing the error upon failure.
 
-Upon success, but if there is no such value for the queried `key`, it returns
-`nil` as its first argument, and no error. The same applies to cached misses
-looked up with this function.
+If there is no value for the queried `key`, it returns `nil` and no error.
 
-Upon success, and if there is such a value for the queried `key`, it returns a
-number indicating the remaining TTL of the cached value. The third returned
-value in that case will be the cached value itself, for convenience.
+If there is a value for the queried `key`, it returns a number indicating the
+remaining TTL of the cached value (in seconds) and no error. If the value for
+`key` has expired but is still in the L2 cache, returned TTL value will be
+negative. Finally, the third returned value in that case will be the cached
+value itself, for convenience.
 
-This method is useful if you want to know whether a value is cached or not. A
-value stored in the L2 cache is considered cached, regardless of whether or not
-it is also set in the L1 cache of the worker. That is because the L1 cache is
-too volatile (as its size unit is a number of slots), and the L2 cache is
+This method is useful when you want to determine if a value is cached. A value
+stored in the L2 cache is considered cached regardless of whether or not it is
+also set in the L1 cache of the worker. That is because the L1 cache is
+considered volatile (as its size unit is a number of slots), and the L2 cache is
 still several orders of magnitude faster than the L3 callback anyway.
 
 As its only intent is to take a "peek" into the cache to determine its warmth
 for a given value, `peek()` does not count as a query like [get()](#get), and
-does not set the value in the L1 cache.
+does not promote the value to the L1 cache.
 
 Example:
 
@@ -761,6 +782,11 @@ ngx.say(ttl)   -- 3
 ngx.say(value) -- "some value"
 ```
 
+**Note:** since mlcache `2.5.0`, it is also possible to call [get()](#get)
+without a callback function in order to "query" the cache. Unlike `peek()`, a
+`get()` call with no callback *will* promote the value to the L1 cache, and
+*will not* return its TTL.
+
 [Back to TOC](#table-of-contents)
 
 set
@@ -865,7 +891,7 @@ request, to make sure they refreshed their L1 cache.
 
 update
 ------
-**syntax:** `ok, err = cache:update()`
+**syntax:** `ok, err = cache:update(timeout?)`
 
 Poll and execute pending cache invalidation events published by other workers.
 
@@ -881,6 +907,12 @@ This method allows a worker to update its L1 cache (by purging values
 considered stale due to an other worker calling `set()`, `delete()`, or
 `purge()`) before processing a request.
 
+This method accepts a `timeout` argument whose unit is seconds and which
+defaults to `0.3` (300ms). The update operation will timeout if it isn't done
+when this threshold in reached. This avoids `update()` from staying on the CPU
+too long in case there are too many events to process. In an eventually
+consistent system, additional events can wait for the next call to be processed.
+
 A typical design pattern is to call `update()` **only once** before each
 request processing. This allows your hot code paths to perform a single shm
 access in the best case scenario: no invalidation events were received, all
diff --git a/lib/resty/mlcache.lua b/lib/resty/mlcache.lua
index 586cf9616..de8eb7417 100644
--- a/lib/resty/mlcache.lua
+++ b/lib/resty/mlcache.lua
@@ -164,7 +164,7 @@ end
 
 
 local _M     = {
-    _VERSION = "2.4.1",
+    _VERSION = "2.5.0",
     _AUTHOR  = "Thibault Charbonnier",
     _LICENSE = "MIT",
     _URL     = "https://github.com/thibaultcha/lua-resty-mlcache",
@@ -821,8 +821,8 @@ function _M:get(key, opts, cb, ...)
         error("key must be a string", 2)
     end
 
-    if type(cb) ~= "function" then
-        error("callback must be a function", 2)
+    if cb ~= nil and type(cb) ~= "function" then
+        error("callback must be nil or a function", 2)
     end
 
     -- worker LRU cache retrieval
@@ -864,7 +864,13 @@ function _M:get(key, opts, cb, ...)
     end
 
     -- not in shm either
-    -- single worker must execute the callback
+
+    if cb == nil then
+        -- no L3 callback, early exit
+        return nil, nil, -1
+    end
+
+    -- L3 callback, single worker to run it
 
     return run_callback(self, key, namespaced_key, data, ttl, neg_ttl,
                         went_stale, l1_serializer, resurrect_ttl,
diff --git a/lib/resty/mlcache/ipc.lua b/lib/resty/mlcache/ipc.lua
index da6174d32..6f00a55fc 100644
--- a/lib/resty/mlcache/ipc.lua
+++ b/lib/resty/mlcache/ipc.lua
@@ -20,6 +20,7 @@ local setmetatable = setmetatable
 
 
 local INDEX_KEY        = "lua-resty-ipc:index"
+local FORCIBLE_KEY     = "lua-resty-ipc:forcible"
 local POLL_SLEEP_RATIO = 2
 
 
@@ -59,19 +60,10 @@ function _M.new(shm, debug)
         return nil, "no such lua_shared_dict: " .. shm
     end
 
-    local idx, err = dict:get(INDEX_KEY)
-    if err then
-        return nil, "failed to get index: " .. err
-    end
-
-    if idx ~= nil and type(idx) ~= "number" then
-        return nil, "index is not a number, shm tampered with"
-    end
-
     local self    = {
         dict      = dict,
         pid       = debug and 0 or worker_pid(),
-        idx       = idx or 0,
+        idx       = 0,
         callbacks = {},
     }
 
@@ -113,11 +105,21 @@ function _M:broadcast(channel, data)
         return nil, "failed to increment index: " .. err
     end
 
-    local ok, err = self.dict:set(idx, marshalled_event)
+    local ok, err, forcible = self.dict:set(idx, marshalled_event)
     if not ok then
         return nil, "failed to insert event in shm: " .. err
     end
 
+    if forcible then
+        -- take note that eviction has started
+        -- we repeat this flagging to avoid this key from ever being
+        -- evicted itself
+        local ok, err = self.dict:set(FORCIBLE_KEY, true)
+        if not ok then
+            return nil, "failed to set forcible flag in shm: " .. err
+        end
+    end
+
     return true
 end
 
@@ -134,17 +136,17 @@ function _M:poll(timeout)
         error("timeout must be a number", 2)
     end
 
-    local idx, err = self.dict:get(INDEX_KEY)
+    local shm_idx, err = self.dict:get(INDEX_KEY)
     if err then
         return nil, "failed to get index: " .. err
     end
 
-    if idx == nil then
+    if shm_idx == nil then
         -- no events to poll yet
         return true
     end
 
-    if type(idx) ~= "number" then
+    if type(shm_idx) ~= "number" then
         return nil, "index is not a number, shm tampered with"
     end
 
@@ -152,9 +154,27 @@ function _M:poll(timeout)
         timeout = 0.3
     end
 
+    if self.idx == 0 then
+        local forcible, err = self.dict:get(FORCIBLE_KEY)
+        if err then
+            return nil, "failed to get forcible flag from shm: " .. err
+        end
+
+        if forcible then
+            -- shm lru eviction occurred, we are likely a new worker
+            -- skip indexes that may have been evicted and resume current
+            -- polling idx
+            self.idx = shm_idx - 1
+        end
+
+    else
+        -- guard: self.idx <= shm_idx
+        self.idx = min(self.idx, shm_idx)
+    end
+
     local elapsed = 0
 
-    for _ = self.idx, idx - 1 do
+    for _ = self.idx, shm_idx - 1 do
         -- fetch event from shm with a retry policy in case
         -- we run our :get() in between another worker's
         -- :incr() and :set()
diff --git a/lua-resty-mlcache-2.4.1-1.rockspec b/lua-resty-mlcache-2.5.0-1.rockspec
similarity index 97%
rename from lua-resty-mlcache-2.4.1-1.rockspec
rename to lua-resty-mlcache-2.5.0-1.rockspec
index 21367f217..857bf52d8 100644
--- a/lua-resty-mlcache-2.4.1-1.rockspec
+++ b/lua-resty-mlcache-2.5.0-1.rockspec
@@ -1,8 +1,8 @@
 package = "lua-resty-mlcache"
-version = "2.4.1-1"
+version = "2.5.0-1"
 source = {
   url = "git://github.com/thibaultcha/lua-resty-mlcache",
-  tag = "2.4.1"
+  tag = "2.5.0"
 }
 description = {
   summary  = "Layered caching library for OpenResty",
diff --git a/t/00-ipc.t b/t/00-ipc.t
index e9a03d2a9..f2e947dc4 100644
--- a/t/00-ipc.t
+++ b/t/00-ipc.t
@@ -57,78 +57,7 @@ no such lua_shared_dict: foo
 
 
 
-=== TEST 2: new() picks up current idx if already set
-This ensures new workers spawned during a master process' lifecycle do not
-attempt to replay all events from index 0.
-https://github.com/thibaultcha/lua-resty-mlcache/issues/87
---- http_config eval
-qq{
-    lua_package_path "$::pwd/lib/?.lua;;";
-    lua_shared_dict  ipc 1m;
-
-    init_by_lua_block {
-        require "resty.core"
-
-        assert(ngx.shared.ipc:set("lua-resty-ipc:index", 42))
-    }
-}
---- config
-    location = /t {
-        content_by_lua_block {
-            local mlcache_ipc = require "resty.mlcache.ipc"
-
-            local ipc, err = mlcache_ipc.new("ipc")
-            if not ipc then
-                error(err)
-            end
-
-            ngx.say(ipc.idx)
-        }
-    }
---- request
-GET /t
---- response_body
-42
---- no_error_log
-[warn]
-[error]
-[crit]
-
-
-
-=== TEST 3: new() checks type of current idx if already set
---- http_config eval
-qq{
-    lua_package_path "$::pwd/lib/?.lua;;";
-    lua_shared_dict  ipc 1m;
-
-    init_by_lua_block {
-        require "resty.core"
-
-        assert(ngx.shared.ipc:set("lua-resty-ipc:index", "42"))
-    }
-}
---- config
-    location = /t {
-        content_by_lua_block {
-            local mlcache_ipc = require "resty.mlcache.ipc"
-
-            local ipc, err = mlcache_ipc.new("ipc")
-            ngx.say(err)
-        }
-    }
---- request
-GET /t
---- response_body
-index is not a number, shm tampered with
---- no_error_log
-[warn]
-[error]
-[crit]
-
-
-
-=== TEST 4: broadcast() sends an event through shm
+=== TEST 2: broadcast() sends an event through shm
 --- http_config eval
 qq{
     $::HttpConfig
@@ -162,7 +91,7 @@ received event from my_channel: hello world
 
 
 
-=== TEST 5: broadcast() runs event callback in protected mode
+=== TEST 3: broadcast() runs event callback in protected mode
 --- http_config eval
 qq{
     $::HttpConfig
@@ -196,7 +125,7 @@ lua entry thread aborted: runtime error
 
 
 
-=== TEST 6: poll() catches invalid timeout arg
+=== TEST 4: poll() catches invalid timeout arg
 --- http_config eval
 qq{
     $::HttpConfig
@@ -225,7 +154,7 @@ timeout must be a number
 
 
 
-=== TEST 7: poll() catches up with all events
+=== TEST 5: poll() catches up with all events
 --- http_config eval
 qq{
     $::HttpConfig
@@ -263,7 +192,62 @@ received event from my_channel: msg 3
 
 
 
-=== TEST 8: poll() does not execute events from self (same pid)
+=== TEST 6: poll() resumes to current idx if events were previously evicted
+This ensures new workers spawned during a master process' lifecycle do not
+attempt to replay all events from index 0.
+https://github.com/thibaultcha/lua-resty-mlcache/issues/87
+https://github.com/thibaultcha/lua-resty-mlcache/issues/93
+--- http_config eval
+qq{
+    lua_package_path "$::pwd/lib/?.lua;;";
+    lua_shared_dict  ipc 32k;
+
+    init_by_lua_block {
+        require "resty.core"
+        local mlcache_ipc = require "resty.mlcache.ipc"
+
+        ipc = assert(mlcache_ipc.new("ipc", true))
+
+        ipc:subscribe("my_channel", function(data)
+            ngx.log(ngx.NOTICE, "my_channel event: ", data)
+        end)
+
+        for i = 1, 32 do
+            -- fill shm, simulating busy workers
+            -- this must trigger eviction for this test to succeed
+            assert(ipc:broadcast("my_channel", string.rep(".", 2^10)))
+        end
+    }
+}
+--- config
+    location = /t {
+        content_by_lua_block {
+            ngx.say("ipc.idx: ", ipc.idx)
+
+            assert(ipc:broadcast("my_channel", "first broadcast"))
+            assert(ipc:broadcast("my_channel", "second broadcast"))
+
+            -- first poll without new() to simulate new worker
+            assert(ipc:poll())
+
+            -- ipc.idx set to shm_idx-1 ("second broadcast")
+            ngx.say("ipc.idx: ", ipc.idx)
+        }
+    }
+--- request
+GET /t
+--- response_body
+ipc.idx: 0
+ipc.idx: 34
+--- error_log
+my_channel event: second broadcast
+--- no_error_log
+my_channel event: first broadcast
+[error]
+
+
+
+=== TEST 7: poll() does not execute events from self (same pid)
 --- http_config eval
 qq{
     $::HttpConfig
@@ -296,7 +280,7 @@ received event from my_channel: hello world
 
 
 
-=== TEST 9: poll() runs all registered callbacks for a channel
+=== TEST 8: poll() runs all registered callbacks for a channel
 --- http_config eval
 qq{
     $::HttpConfig
@@ -340,7 +324,7 @@ callback 3 from my_channel: hello world
 
 
 
-=== TEST 10: poll() exits when no event to poll
+=== TEST 9: poll() exits when no event to poll
 --- http_config eval
 qq{
     $::HttpConfig
@@ -371,7 +355,7 @@ callback from my_channel: hello world
 
 
 
-=== TEST 11: poll() runs all callbacks from all channels
+=== TEST 10: poll() runs all callbacks from all channels
 --- http_config eval
 qq{
     $::HttpConfig
@@ -424,7 +408,7 @@ callback 2 from other_channel: hello ipc 2
 
 
 
-=== TEST 12: poll() catches tampered shm (by third-party users)
+=== TEST 11: poll() catches tampered shm (by third-party users)
 --- http_config eval
 qq{
     $::HttpConfig
@@ -457,7 +441,7 @@ index is not a number, shm tampered with
 
 
 
-=== TEST 13: poll() retries getting an event until timeout
+=== TEST 12: poll() retries getting an event until timeout
 --- http_config eval
 qq{
     $::HttpConfig
@@ -502,7 +486,7 @@ GET /t
 
 
 
-=== TEST 14: poll() reaches custom timeout
+=== TEST 13: poll() reaches custom timeout
 --- http_config eval
 qq{
     $::HttpConfig
@@ -542,7 +526,7 @@ GET /t
 
 
 
-=== TEST 15: poll() logs errors and continue if event has been tampered with
+=== TEST 14: poll() logs errors and continue if event has been tampered with
 --- http_config eval
 qq{
     $::HttpConfig
@@ -580,7 +564,7 @@ GET /t
 
 
 
-=== TEST 16: poll() is safe to be called in contexts that don't support ngx.sleep()
+=== TEST 15: poll() is safe to be called in contexts that don't support ngx.sleep()
 --- http_config eval
 qq{
     $::HttpConfig
@@ -624,6 +608,52 @@ GET /t
 
 
 
+=== TEST 16: poll() guards self.idx from growing beyond the current shm idx
+--- http_config eval
+qq{
+    $::HttpConfig
+
+    init_worker_by_lua_block {
+        local mlcache_ipc = require "resty.mlcache.ipc"
+
+        ipc = assert(mlcache_ipc.new("ipc", true))
+
+        ipc:subscribe("my_channel", function(data)
+            ngx.log(ngx.NOTICE, "callback from my_channel: ", data)
+        end)
+    }
+}
+--- config
+    location = /t {
+        content_by_lua_block {
+            assert(ipc:broadcast("other_channel", ""))
+            assert(ipc:poll())
+            assert(ipc:broadcast("my_channel", "fist broadcast"))
+            assert(ipc:broadcast("other_channel", ""))
+            assert(ipc:broadcast("my_channel", "second broadcast"))
+
+            -- shm idx is 5, let's mess with the instance's idx
+            ipc.idx = 10
+            assert(ipc:poll())
+
+            -- we may have skipped the above events, but we are able to resume polling
+            assert(ipc:broadcast("other_channel", ""))
+            assert(ipc:broadcast("my_channel", "third broadcast"))
+            assert(ipc:poll())
+        }
+    }
+--- request
+GET /t
+--- ignore_response_body
+--- error_log
+callback from my_channel: third broadcast
+--- no_error_log
+callback from my_channel: first broadcast
+callback from my_channel: second broadcast
+[error]
+
+
+
 === TEST 17: poll() JITs
 --- http_config eval
 qq{
diff --git a/t/02-get.t b/t/02-get.t
index 17bf14093..40de0efc3 100644
--- a/t/02-get.t
+++ b/t/02-get.t
@@ -72,7 +72,7 @@ key must be a string
 
 
 
-=== TEST 2: get() validates callback
+=== TEST 2: get() accepts callback as nil or function
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -85,7 +85,12 @@ key must be a string
                 return
             end
 
-            local ok, err = pcall(cache.get, cache, "key")
+            local ok, err = pcall(cache.get, cache, "key", nil, nil)
+            if not ok then
+                ngx.say(err)
+            end
+
+            local ok, err = pcall(cache.get, cache, "key", nil, function() end)
             if not ok then
                 ngx.say(err)
             end
@@ -94,14 +99,13 @@ key must be a string
 --- request
 GET /t
 --- response_body
-callback must be a function
+
 --- no_error_log
 [error]
 
 
 
-=== TEST 3: get() validates opts
---- SKIP: no options yet
+=== TEST 3: get() rejects callbacks not nil or function
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -114,7 +118,41 @@ callback must be a function
                 return
             end
 
-            local ok, err = pcall(cache.get, cache, "key", function() end, 0)
+            local ok, err = pcall(cache.get, cache, "key", nil, "not a function")
+            if not ok then
+                ngx.say(err)
+            end
+
+            local ok, err = pcall(cache.get, cache, "key", nil, false)
+            if not ok then
+                ngx.say(err)
+            end
+        }
+    }
+--- request
+GET /t
+--- response_body
+callback must be nil or a function
+callback must be nil or a function
+--- no_error_log
+[error]
+
+
+
+=== TEST 4: get() validates opts
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local mlcache = require "resty.mlcache"
+
+            local cache, err = mlcache.new("my_mlcache", "cache_shm")
+            if not cache then
+                ngx.log(ngx.ERR, err)
+                return
+            end
+
+            local ok, err = pcall(cache.get, cache, "key", "opts")
             if not ok then
                 ngx.say(err)
             end
@@ -129,7 +167,7 @@ opts must be a table
 
 
 
-=== TEST 4: get() calls callback in protected mode with stack traceback
+=== TEST 5: get() calls callback in protected mode with stack traceback
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -164,7 +202,7 @@ stack traceback:
 
 
 
-=== TEST 5: get() is resilient to callback runtime errors with non-string arguments
+=== TEST 6: get() is resilient to callback runtime errors with non-string arguments
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -198,7 +236,7 @@ callback threw an error: table: 0x[0-9a-fA-F]+
 
 
 
-=== TEST 6: get() caches a number
+=== TEST 7: get() caches a number
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -259,7 +297,7 @@ from shm: number 123
 
 
 
-=== TEST 7: get() caches a boolean (true)
+=== TEST 8: get() caches a boolean (true)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -320,7 +358,7 @@ from shm: boolean true
 
 
 
-=== TEST 8: get() caches a boolean (false)
+=== TEST 9: get() caches a boolean (false)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -381,7 +419,7 @@ from shm: boolean false
 
 
 
-=== TEST 9: get() caches nil
+=== TEST 10: get() caches nil
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -442,7 +480,7 @@ from shm: nil nil
 
 
 
-=== TEST 10: get() caches nil in 'shm_miss' if specified
+=== TEST 11: get() caches nil in 'shm_miss' if specified
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -523,7 +561,7 @@ value in lru is a sentinel nil value: true
 
 
 
-=== TEST 11: get() caches a string
+=== TEST 12: get() caches a string
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -584,7 +622,7 @@ from shm: string hello world
 
 
 
-=== TEST 12: get() caches a table
+=== TEST 13: get() caches a table
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -649,7 +687,7 @@ from shm: table world bar
 
 
 
-=== TEST 13: get() errors when caching an unsupported type
+=== TEST 14: get() errors when caching an unsupported type
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -682,7 +720,7 @@ qr/\[error\] .*?mlcache\.lua:\d+: cannot cache value of type userdata/
 
 
 
-=== TEST 14: get() calls callback with args
+=== TEST 15: get() calls callback with args
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -717,7 +755,7 @@ GET /t
 
 
 
-=== TEST 15: get() caches hit for 'ttl' from LRU (in ms)
+=== TEST 16: get() caches hit for 'ttl' from LRU (in ms)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -755,7 +793,7 @@ in callback
 
 
 
-=== TEST 16: get() caches miss (nil) for 'neg_ttl' from LRU (in ms)
+=== TEST 17: get() caches miss (nil) for 'neg_ttl' from LRU (in ms)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -799,7 +837,7 @@ in callback
 
 
 
-=== TEST 17: get() caches for 'opts.ttl' from LRU (in ms)
+=== TEST 18: get() caches for 'opts.ttl' from LRU (in ms)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -837,7 +875,7 @@ in callback
 
 
 
-=== TEST 18: get() caches for 'opts.neg_ttl' from LRU (in ms)
+=== TEST 19: get() caches for 'opts.neg_ttl' from LRU (in ms)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -878,7 +916,7 @@ in callback
 
 
 
-=== TEST 19: get() with ttl of 0 means indefinite caching
+=== TEST 20: get() with ttl of 0 means indefinite caching
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -925,7 +963,7 @@ in shm after exp: 123
 
 
 
-=== TEST 20: get() with neg_ttl of 0 means indefinite caching for nil values
+=== TEST 21: get() with neg_ttl of 0 means indefinite caching for nil values
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -974,7 +1012,7 @@ in shm after exp: nil
 
 
 
-=== TEST 21: get() errors when ttl < 0
+=== TEST 22: get() errors when ttl < 0
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1007,7 +1045,7 @@ opts.ttl must be >= 0
 
 
 
-=== TEST 22: get() errors when neg_ttl < 0
+=== TEST 23: get() errors when neg_ttl < 0
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1040,7 +1078,7 @@ opts.neg_ttl must be >= 0
 
 
 
-=== TEST 23: get() shm -> LRU caches for 'opts.ttl - since' in ms
+=== TEST 24: get() shm -> LRU caches for 'opts.ttl - since' in ms
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1098,7 +1136,7 @@ is stale in LRU: 123
 
 
 
-=== TEST 24: get() shm -> LRU caches non-nil for 'indefinite' if ttl is 0
+=== TEST 25: get() shm -> LRU caches non-nil for 'indefinite' if ttl is 0
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1142,7 +1180,7 @@ is not expired in LRU: 123
 
 
 
-=== TEST 25: get() shm -> LRU caches for 'opts.neg_ttl - since' in ms
+=== TEST 26: get() shm -> LRU caches for 'opts.neg_ttl - since' in ms
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1202,7 +1240,7 @@ is stale in LRU: table: \S+
 
 
 
-=== TEST 26: get() shm -> LRU caches nil for 'indefinite' if neg_ttl is 0
+=== TEST 27: get() shm -> LRU caches nil for 'indefinite' if neg_ttl is 0
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1245,7 +1283,7 @@ is stale in LRU: nil
 
 
 
-=== TEST 27: get() returns hit level
+=== TEST 28: get() returns hit level
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1283,7 +1321,7 @@ hit level from shm: 2
 
 
 
-=== TEST 28: get() returns hit level for nil hits
+=== TEST 29: get() returns hit level for nil hits
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1321,7 +1359,7 @@ hit level from shm: 2
 
 
 
-=== TEST 29: get() returns hit level for boolean false hits
+=== TEST 30: get() returns hit level for boolean false hits
 --- skip_eval: 3: t::Util::skip_openresty('<', '1.11.2.3')
 --- http_config eval: $::HttpConfig
 --- config
@@ -1360,7 +1398,7 @@ hit level from shm: 2
 
 
 
-=== TEST 30: get() JITs when hit coming from LRU
+=== TEST 31: get() JITs when hit coming from LRU
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1390,7 +1428,7 @@ qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):10 loop\]/
 
 
 
-=== TEST 31: get() JITs when hit of scalar value coming from shm
+=== TEST 32: get() JITs when hit of scalar value coming from shm
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1454,8 +1492,8 @@ GET /t
 
 
 
-=== TEST 32: get() JITs when hit of table value coming from shm
---- SKIP: blocked until custom table serializer
+=== TEST 33: get() JITs when hit of table value coming from shm
+--- SKIP: blocked until l2_serializer
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1488,7 +1526,7 @@ qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):18 loop\]/
 
 
 
-=== TEST 33: get() JITs when miss coming from LRU
+=== TEST 34: get() JITs when miss coming from LRU
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1519,7 +1557,7 @@ qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):10 loop\]/
 
 
 
-=== TEST 34: get() JITs when miss coming from shm
+=== TEST 35: get() JITs when miss coming from shm
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1552,7 +1590,7 @@ qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):10 loop\]/
 
 
 
-=== TEST 35: get() callback can return nil + err (string)
+=== TEST 36: get() callback can return nil + err (string)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1592,7 +1630,7 @@ cb2 return values: foo an error occurred again
 
 
 
-=== TEST 36: get() callback can return nil + err (non-string) safely
+=== TEST 37: get() callback can return nil + err (non-string) safely
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1631,7 +1669,7 @@ cb2 return values: foo table: 0x[[:xdigit:]]+
 
 
 
-=== TEST 37: get() callback can return nil + err (table) and will call __tostring
+=== TEST 38: get() callback can return nil + err (table) and will call __tostring
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1664,7 +1702,7 @@ cb return values: nil hello from __tostring
 
 
 
-=== TEST 38: get() callback's 3th return value can override the ttl
+=== TEST 39: get() callback's 3th return value can override the ttl
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1715,7 +1753,7 @@ in callback 2
 
 
 
-=== TEST 39: get() callback's 3th return value can override the neg_ttl
+=== TEST 40: get() callback's 3th return value can override the neg_ttl
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1766,7 +1804,7 @@ in callback 2
 
 
 
-=== TEST 40: get() ignores invalid callback 3rd return value (not number)
+=== TEST 41: get() ignores invalid callback 3rd return value (not number)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1845,7 +1883,7 @@ in positive callback
 
 
 
-=== TEST 41: get() passes 'resty_lock_opts' for L3 calls
+=== TEST 42: get() passes 'resty_lock_opts' for L3 calls
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1888,7 +1926,7 @@ was given 'opts.resty_lock_opts': true
 
 
 
-=== TEST 42: get() errors on lock timeout
+=== TEST 43: get() errors on lock timeout
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -1968,7 +2006,7 @@ hit_lvl: 1
 
 
 
-=== TEST 43: get() returns data even if failed to set in shm
+=== TEST 44: get() returns data even if failed to set in shm
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2020,7 +2058,7 @@ qr/\[warn\] .*? could not write to lua_shared_dict 'cache_shm' after 3 tries \(n
 
 
 
-=== TEST 44: get() errors on invalid opts.shm_set_tries
+=== TEST 45: get() errors on invalid opts.shm_set_tries
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2060,7 +2098,7 @@ opts.shm_set_tries must be >= 1
 
 
 
-=== TEST 45: get() with default shm_set_tries to LRU evict items when a large value is being cached
+=== TEST 46: get() with default shm_set_tries to LRU evict items when a large value is being cached
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2131,7 +2169,7 @@ callback was called: 1 times
 
 
 
-=== TEST 46: get() respects instance opts.shm_set_tries to LRU evict items when a large value is being cached
+=== TEST 47: get() respects instance opts.shm_set_tries to LRU evict items when a large value is being cached
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2204,7 +2242,7 @@ callback was called: 1 times
 
 
 
-=== TEST 47: get() accepts opts.shm_set_tries to LRU evict items when a large value is being cached
+=== TEST 48: get() accepts opts.shm_set_tries to LRU evict items when a large value is being cached
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2277,7 +2315,7 @@ callback was called: 1 times
 
 
 
-=== TEST 48: get() caches data in L1 LRU even if failed to set in shm
+=== TEST 49: get() caches data in L1 LRU even if failed to set in shm
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2341,7 +2379,7 @@ is stale: true
 
 
 
-=== TEST 49: get() does not cache value in LRU indefinitely when retrieved from shm on last ms (see GH PR #58)
+=== TEST 50: get() does not cache value in LRU indefinitely when retrieved from shm on last ms (see GH PR #58)
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2406,7 +2444,7 @@ GET /t
 
 
 
-=== TEST 50: get() bypass cache for negative callback TTL
+=== TEST 51: get() bypass cache for negative callback TTL
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -2470,3 +2508,195 @@ in negative callback
 in negative callback
 --- no_error_log
 [error]
+
+
+
+=== TEST 52: get() nil callback returns positive cached items from L1/L2
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local mlcache = require "resty.mlcache"
+
+            local cache = assert(mlcache.new("my_mlcache", "cache_shm"))
+
+            -- miss lookup
+
+            local data, err, hit_lvl = cache:get("key")
+            if err then
+                ngx.log(ngx.ERR, err)
+            end
+            ngx.say("-> miss")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+
+            -- cache an item
+
+            local _, err = cache:get("key", nil, function() return 123 end)
+            if err then
+                ngx.log(ngx.ERR, err)
+            end
+
+            -- hit from lru
+
+            local data, err, hit_lvl = cache:get("key")
+            ngx.say()
+            ngx.say("-> from LRU")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+
+            -- hit from shm
+
+            cache.lru:delete("key")
+
+            local data, err, hit_lvl = cache:get("key")
+            ngx.say()
+            ngx.say("-> from shm")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+
+            -- promoted to lru again
+
+            local data, err, hit_lvl = cache:get("key")
+            ngx.say()
+            ngx.say("-> promoted to LRU")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+        }
+    }
+--- request
+GET /t
+--- response_body
+-> miss
+data: nil
+err: nil
+hit_lvl: -1
+
+-> from LRU
+data: 123
+err: nil
+hit_lvl: 1
+
+-> from shm
+data: 123
+err: nil
+hit_lvl: 2
+
+-> promoted to LRU
+data: 123
+err: nil
+hit_lvl: 1
+--- no_error_log
+[error]
+
+
+
+=== TEST 53: get() nil callback returns negative cached items from L1/L2
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local mlcache = require "resty.mlcache"
+
+            local cache = assert(mlcache.new("my_mlcache", "cache_shm"))
+
+            -- miss lookup
+
+            local data, err, hit_lvl = cache:get("key")
+            if err then
+                ngx.log(ngx.ERR, err)
+            end
+            ngx.say("-> miss")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+
+            -- cache an item
+
+            local _, err = cache:get("key", nil, function() return nil end)
+            if err then
+                ngx.log(ngx.ERR, err)
+            end
+
+            -- hit from lru
+
+            local data, err, hit_lvl = cache:get("key")
+            ngx.say()
+            ngx.say("-> from LRU")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+
+            -- hit from shm
+
+            cache.lru:delete("key")
+
+            local data, err, hit_lvl = cache:get("key")
+            ngx.say()
+            ngx.say("-> from shm")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+
+            -- promoted to lru again
+
+            local data, err, hit_lvl = cache:get("key")
+            ngx.say()
+            ngx.say("-> promoted to LRU")
+            ngx.say("data: ", data)
+            ngx.say("err: ", err)
+            ngx.say("hit_lvl: ", hit_lvl)
+        }
+    }
+--- request
+GET /t
+--- response_body
+-> miss
+data: nil
+err: nil
+hit_lvl: -1
+
+-> from LRU
+data: nil
+err: nil
+hit_lvl: 1
+
+-> from shm
+data: nil
+err: nil
+hit_lvl: 2
+
+-> promoted to LRU
+data: nil
+err: nil
+hit_lvl: 1
+--- no_error_log
+[error]
+
+
+
+=== TEST 54: get() JITs on misses without a callback
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local mlcache = require "resty.mlcache"
+
+            local cache = assert(mlcache.new("my_mlcache", "cache_shm"))
+
+            for i = 1, 10e3 do
+                cache:get("key")
+            end
+        }
+    }
+--- request
+GET /t
+--- ignore_response_body
+--- error_log eval
+qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):6 loop\]/
+--- no_error_log
+[error]
diff --git a/t/03-peek.t b/t/03-peek.t
index fdeb96c1d..bee4b9da0 100644
--- a/t/03-peek.t
+++ b/t/03-peek.t
@@ -151,7 +151,47 @@ ttl: 18
 
 
 
-=== TEST 4: peek() returns remaining ttl if shm_miss is specified
+=== TEST 4: peek() returns a negative ttl when a key expired
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local mlcache = require "resty.mlcache"
+
+            local cache = assert(mlcache.new("my_mlcache", "cache_shm"))
+
+            local function cb()
+                return nil
+            end
+
+            local val, err = cache:get("my_key", { neg_ttl = 0 }, cb)
+            if err then
+                ngx.log(ngx.ERR, err)
+                return
+            end
+
+            ngx.sleep(1)
+
+            local ttl = assert(cache:peek("my_key"))
+            ngx.say("ttl: ", math.ceil(ttl))
+
+            ngx.sleep(1)
+
+            local ttl = assert(cache:peek("my_key"))
+            ngx.say("ttl: ", math.ceil(ttl))
+        }
+    }
+--- request
+GET /t
+--- response_body
+ttl: -1
+ttl: -2
+--- no_error_log
+[error]
+
+
+
+=== TEST 5: peek() returns remaining ttl if shm_miss is specified
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -201,7 +241,7 @@ ttl: 18
 
 
 
-=== TEST 5: peek() returns the value if a key has been fetched before
+=== TEST 6: peek() returns the value if a key has been fetched before
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -261,7 +301,7 @@ ttl: \d* nil_val: nil
 
 
 
-=== TEST 6: peek() returns the value if shm_miss is specified
+=== TEST 7: peek() returns the value if shm_miss is specified
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -300,7 +340,7 @@ ttl: \d* nil_val: nil
 
 
 
-=== TEST 7: peek() JITs on hit
+=== TEST 8: peek() JITs on hit
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -332,7 +372,7 @@ qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):13 loop\]/
 
 
 
-=== TEST 8: peek() JITs on miss
+=== TEST 9: peek() JITs on miss
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -360,7 +400,7 @@ qr/\[TRACE\s+\d+ content_by_lua\(nginx\.conf:\d+\):6 loop\]/
 
 
 
-=== TEST 9: peek() returns nil if a value expired
+=== TEST 10: peek() returns nil if a value expired
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -401,7 +441,7 @@ stale: nil
 
 
 
-=== TEST 10: peek() returns nil if a value expired in 'shm_miss'
+=== TEST 11: peek() returns nil if a value expired in 'shm_miss'
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -448,7 +488,7 @@ stale: nil
 
 
 
-=== TEST 11: peek() accepts stale arg and returns stale values
+=== TEST 12: peek() accepts stale arg and returns stale values
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -489,7 +529,7 @@ stale: true
 
 
 
-=== TEST 12: peek() accepts stale arg and returns stale values from 'shm_miss'
+=== TEST 13: peek() accepts stale arg and returns stale values from 'shm_miss'
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -536,7 +576,7 @@ stale: true
 
 
 
-=== TEST 13: peek() does not evict stale items from L2 shm
+=== TEST 14: peek() does not evict stale items from L2 shm
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
@@ -581,7 +621,7 @@ data: 123
 
 
 
-=== TEST 14: peek() does not evict stale negative data from L2 shm_miss
+=== TEST 15: peek() does not evict stale negative data from L2 shm_miss
 --- http_config eval: $::HttpConfig
 --- config
     location = /t {
diff --git a/t/09-isolation.t b/t/09-isolation.t
index 9e88d5b18..0ce0b40b9 100644
--- a/t/09-isolation.t
+++ b/t/09-isolation.t
@@ -87,7 +87,7 @@ lua-resty-lru instances are the same: false
 
             -- prove LRU survived
 
-            ngx.say(cache_2.lru:get("key"))
+            ngx.say((cache_2.lru:get("key")))
 
             -- GC cache_2 (and the LRU this time, since no more references)
 
@@ -101,7 +101,7 @@ lua-resty-lru instances are the same: false
 
             -- this is a new LRU, it has nothing in it
 
-            ngx.say(cache_2.lru:get("key"))
+            ngx.say((cache_2.lru:get("key")))
         }
     }
 --- request
diff --git a/t/13-get_bulk.t b/t/13-get_bulk.t
index 428ff1564..7b6498a91 100644
--- a/t/13-get_bulk.t
+++ b/t/13-get_bulk.t
@@ -128,6 +128,15 @@ key at index 5 must be a string for operation 2 (got boolean)
             local mlcache = require "resty.mlcache"
             local cache = assert(mlcache.new("my_mlcache", "cache_shm"))
 
+            local pok, perr = pcall(cache.get_bulk, cache, {
+                "key_b", nil, nil, nil,
+                "key_a", nil, function() return 1 end, nil,
+                n = 2,
+            })
+            if not pok then
+                ngx.say(perr)
+            end
+
             local pok, perr = pcall(cache.get_bulk, cache, {
                 "key_a", nil, function() return 1 end, nil,
                 "key_b", nil, false, nil,
@@ -141,6 +150,7 @@ key at index 5 must be a string for operation 2 (got boolean)
 --- request
 GET /t
 --- response_body
+callback at index 3 must be a function for operation 1 (got nil)
 callback at index 7 must be a function for operation 2 (got boolean)
 --- no_error_log
 [error]
diff --git a/t/Util.pm b/t/Util.pm
index d68748a5e..f8a14f3b6 100644
--- a/t/Util.pm
+++ b/t/Util.pm
@@ -1,3 +1,4 @@
+use strict;
 package t::Util;
 
 sub get_openresty_canon_version (@) {
@@ -46,3 +47,5 @@ our @EXPORT = qw(
 );
 
 1;
+
+# vim: set ft=perl: