diff --git a/pyproject.toml b/pyproject.toml
index fae02e8..6d39c8b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -57,4 +57,5 @@ exclude_lines = [
     "def __repr__",
     "def __str__",
     "def __repr_args__",
+    "except ImportError:", # Don't complain about import fallback
 ]
diff --git a/src/graia/broadcast/interfaces/dispatcher.py b/src/graia/broadcast/interfaces/dispatcher.py
index 1f1a0f9..48a89eb 100644
--- a/src/graia/broadcast/interfaces/dispatcher.py
+++ b/src/graia/broadcast/interfaces/dispatcher.py
@@ -84,7 +84,7 @@ def event(self) -> T_Event:
     @property
     def is_optional(self) -> bool:
         anno = self.annotation
-        return get_origin(anno) is Union and None in get_args(anno)
+        return get_origin(anno) is Union and type(None) in get_args(anno)
 
     @property
     def is_annotated(self) -> bool:
diff --git a/src/test/dispatch.py b/src/test/dispatch.py
index 8e92ae9..ac498f6 100644
--- a/src/test/dispatch.py
+++ b/src/test/dispatch.py
@@ -6,18 +6,30 @@
 from graia.broadcast.entities.dispatcher import BaseDispatcher
 from graia.broadcast.entities.event import Dispatchable
 from graia.broadcast.entities.signatures import Force
+from graia.broadcast.exceptions import ExecutionStop, RequirementCrashed
 from graia.broadcast.interfaces.dispatcher import DispatcherInterface
 
 
-class TestDispatcher(BaseDispatcher):
-    @staticmethod
-    async def catch(interface: DispatcherInterface):
+class RandomDispatcher(BaseDispatcher):
+    def __init__(self, t: bool = False) -> None:
+        self.second_exec = t
+
+    async def catch(self, interface: DispatcherInterface):
         if interface.name == "p":
             return "P_dispatcher"
         elif interface.name == "f":
+            if self.second_exec:
+                return
+            self.second_exec = True
             return Force(2)
 
 
+class CrashDispatcher(BaseDispatcher):
+    @staticmethod
+    async def catch(i: DispatcherInterface):
+        i.crash()
+
+
 class TestEvent(Dispatchable):
     class Dispatcher(BaseDispatcher):
         @staticmethod
@@ -36,8 +48,21 @@ async def test_lookup_directly():
 
     dii = DispatcherInterface(bcc, [])
 
-    assert await dii.lookup_by_directly(TestDispatcher, "p", None, None) == "P_dispatcher"
-    assert await dii.lookup_by_directly(TestDispatcher, "f", None, None) == 2
+    assert await dii.lookup_by_directly(RandomDispatcher(), "p", None, None) == "P_dispatcher"
+    assert await dii.lookup_by_directly(RandomDispatcher(), "f", None, None) == 2
+
+
+@pytest.mark.asyncio
+async def test_crash():
+    bcc = Broadcast(
+        loop=asyncio.get_running_loop(),
+    )
+
+    dii = DispatcherInterface(bcc, [])
+    with pytest.raises(RequirementCrashed):
+        await dii.lookup_by_directly(CrashDispatcher, "u", None, None)
+    with pytest.raises(ExecutionStop):
+        dii.stop()
 
 
 @pytest.mark.asyncio
@@ -48,8 +73,8 @@ async def test_insert():
 
     dii = DispatcherInterface(bcc, [])
 
-    t_a = TestDispatcher()
-    t_b = TestDispatcher()
+    t_a = RandomDispatcher()
+    t_b = RandomDispatcher()
     dii.inject_execution_raw(t_a, t_b)
     assert dii.dispatchers == [t_b, t_a]
 
@@ -83,7 +108,7 @@ async def test_dispatcher_catch():
 
     executed = []
 
-    @bcc.receiver(TestEvent, dispatchers=[TestDispatcher])
+    @bcc.receiver(TestEvent, dispatchers=[RandomDispatcher(), RandomDispatcher()])
     async def _1(f, b: Broadcast, i: DispatcherInterface):
         assert f == 2
         assert b is bcc
@@ -91,8 +116,9 @@ async def _1(f, b: Broadcast, i: DispatcherInterface):
         executed.append(1)
 
     await bcc.postEvent(TestEvent())
+    await bcc.postEvent(TestEvent())
 
-    assert len(executed) == 1
+    assert len(executed) == 2
 
 
 @pytest.mark.asyncio
@@ -104,7 +130,7 @@ async def test_dispatcher_priority():
 
     executed = []
 
-    @bcc.receiver(TestEvent, dispatchers=[TestDispatcher])
+    @bcc.receiver(TestEvent, dispatchers=[RandomDispatcher])
     async def _2(ster, p):
         assert ster == "1"
         assert p == "P_dispatcher"