[minor] Clean up optional in type map return type (#22254)

Authored by Codex

Author: hauntsaninja

mypy/checker_shared.py

@@ -260,7 +260,7 @@ def narrow_type_by_identity_equality(
         operand_types: list[Type],
         expr_indices: list[int],
         narrowable_indices: AbstractSet[int],
-    ) -> tuple[dict[Expression, Type] | None, dict[Expression, Type] | None]:
+    ) -> tuple[dict[Expression, Type], dict[Expression, Type]]:
         raise NotImplementedError
 
     @abstractmethod

mypy/checkpattern.py

@@ -211,8 +211,8 @@ def visit_value_pattern(self, o: ValuePattern) -> PatternType:
         ok_map, rest_map = self.chk.narrow_type_by_identity_equality(
             "==", [node, TempNode(typ)], [current_type, typ], [0, 1], {0}
         )
-        ok_type = ok_map.get(node, current_type) if ok_map is not None else UninhabitedType()
-        rest_type = rest_map.get(node, current_type) if rest_map is not None else UninhabitedType()
+        ok_type = ok_map.get(node, current_type)
+        rest_type = rest_map.get(node, current_type)
         return PatternType(ok_type, rest_type, {})
 
     def visit_singleton_pattern(self, o: SingletonPattern) -> PatternType: