Fixed bug in callable type narrowing logic where the union of the type includes None.

packages/pyright-internal/src/analyzer/typeEvaluator.ts

@@ -12660,6 +12660,7 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                     return isPositiveTest ? subtype : undefined;
                 }
 
+                case TypeCategory.None:
                 case TypeCategory.Module: {
                     return isPositiveTest ? undefined : subtype;
                 }

packages/pyright-internal/src/tests/samples/typeNarrowing9.py

@@ -1,7 +1,7 @@
 # This sample tests the type engine's narrowing logic for
 # callable expressions.
 
-from typing import Callable, Type, Union
+from typing import Callable, Optional, Type, Union
 
 
 class CallableObj:
@@ -29,3 +29,8 @@ if callable(q):
 if not callable(q):
     a = q + 3
 
+
+def g(a: Optional[Callable[[int], int]]):
+    if callable(a):
+        a(3)
+