support 'return None' and 'yield None'

Author: Ilya Priven

mypy/checker.py

@@ -1072,10 +1072,10 @@ def _is_empty_generator(self, func: FuncItem) -> bool:
         return (
             len(body := func.body.body) == 2
             and isinstance(ret_stmt := body[0], ReturnStmt)
-            and ret_stmt.expr is None
+            and (ret_stmt.expr is None or is_literal_none(ret_stmt.expr))
             and isinstance(expr_stmt := body[1], ExpressionStmt)
             and isinstance(yield_expr := expr_stmt.expr, YieldExpr)
-            and yield_expr.expr is None
+            and (yield_expr.expr is None or is_literal_none(yield_expr.expr))
         )
 
     def check_func_def(

test-data/unit/check-unreachable-code.test

@@ -1454,3 +1454,11 @@ from typing import Generator
 def f() -> Generator[None, None, None]:
     return
     yield
+
+[case testIntentionallyEmptyGenerator_None]
+# flags: --warn-unreachable
+from typing import Generator
+
+def f() -> Generator[None, None, None]:
+    return None
+    yield None