nil-collection should be treated as empty array in template

lib/jbuilder.rb

@@ -92,7 +92,7 @@ def set!(key, value = BLANK, *args, &block)
         # { "age": 32 }
         value
       end
-    elsif value.respond_to?(:map)
+    elsif value.respond_to?(:map) || ((opts = args.last).respond_to?(:map) && opts[:as])
       # json.comments @post.comments, :content, :created_at
       # { "comments": [ { "content": "hello", "created_at": "..." }, { "content": "world", "created_at": "..." } ] }
       _scope{ array! value, *args }
@@ -221,7 +221,7 @@ def child!
   #   json.array! [1, 2, 3]
   #
   #   [1,2,3]
-  def array!(collection, *attributes, &block)
+  def array!(collection = [], *attributes, &block)
     @attributes = if block && block.arity == 2
       _two_arguments_map_collection(collection, &block)
     elsif block

lib/jbuilder/jbuilder_template.rb

@@ -22,13 +22,15 @@ def partial!(name_or_options, locals = {})
       options = { :partial => name_or_options, :locals => locals }
       as = locals.delete(:as)
       options[:as] = as if as.present?
-      options[:collection] = locals[:collection]
+      options[:collection] = locals[:collection] if locals.key?(:collection)
     end
 
+    options[:collection] ||= [] if options.key?(:collection)
+
     _handle_partial_options options
   end
 
-  def array!(collection, *attributes, &block)
+  def array!(collection = [], *attributes, &block)
     options = attributes.extract_options!
 
     if options.key?(:partial)

test/jbuilder_template_test.rb

@@ -110,6 +110,14 @@ def assert_collection_rendered(json, context = nil)
     assert_collection_rendered json
   end
 
+  test 'partial! renders as empty array for nil-collection' do
+    json = render_jbuilder <<-JBUILDER
+      json.partial! 'blog_post', :collection => nil, :as => :blog_post
+    JBUILDER
+
+    assert_equal '[]', json
+  end
+
   test 'partial! renders collection (alt. syntax)' do
     json = render_jbuilder <<-JBUILDER
       json.partial! :partial => 'blog_post', :collection => BLOG_POST_COLLECTION, :as => :blog_post
@@ -118,6 +126,14 @@ def assert_collection_rendered(json, context = nil)
     assert_collection_rendered json
   end
 
+  test 'partial! renders as empty array for nil-collection (alt. syntax)' do
+    json = render_jbuilder <<-JBUILDER
+      json.partial! :partial => 'blog_post', :collection => nil, :as => :blog_post
+    JBUILDER
+
+    assert_equal '[]', json
+  end
+
   test 'render array of partials' do
     json = render_jbuilder <<-JBUILDER
       json.array! BLOG_POST_COLLECTION, :partial => 'blog_post', :as => :blog_post
@@ -126,6 +142,14 @@ def assert_collection_rendered(json, context = nil)
     assert_collection_rendered json
   end
 
+  test 'render array of partials as empty array with nil-collection' do
+    json = render_jbuilder <<-JBUILDER
+      json.array! nil, :partial => 'blog_post', :as => :blog_post
+    JBUILDER
+
+    assert_equal '[]', json
+  end
+
   test 'render array if partials as a value' do
     json = render_jbuilder <<-JBUILDER
       json.posts BLOG_POST_COLLECTION, :partial => 'blog_post', :as => :blog_post
@@ -134,6 +158,14 @@ def assert_collection_rendered(json, context = nil)
     assert_collection_rendered json, 'posts'
   end
 
+  test 'render as empty array if partials as a nil value' do
+    json = render_jbuilder <<-JBUILDER
+      json.posts nil, :partial => 'blog_post', :as => :blog_post
+    JBUILDER
+
+    assert_equal '{"posts":[]}', json
+  end
+
   test 'fragment caching a JSON object' do
     undef_context_methods :fragment_name_with_digest, :cache_fragment_name