check primer

Author: hauntsaninja

mypy/checker.py

@@ -6736,7 +6736,8 @@ def narrow_type_by_identity_equality(
                     # However, for non-value targets, we cannot do this narrowing,
                     # and so we ignore else_map
                     # e.g. if (x: str | None) != (y: str), we cannot narrow x to None
-                    all_if_maps.append(if_map)
+                    if if_map is not None:  # TODO: this is incorrect
+                        all_if_maps.append(if_map)
 
         # Handle narrowing for operands with custom __eq__ methods specially
         # In most cases, we won't be able to do any narrowing