Issue #15767: Add an explicit test for raising ModuleNotFoundError

when None in sys.modules.

Lib/test/test_importlib/import_/test_api.py

@@ -26,6 +26,13 @@ class APITest(unittest.TestCase):
         with self.assertRaises(ModuleNotFoundError):
             util.import_('some module that does not exist')
 
+    def test_raises_ModuleNotFoundError_for_None(self):
+        # None in sys.modules should raise ModuleNotFoundError.
+        with importlib_test_util.uncache('not_here'):
+            sys.modules['not_here'] = None
+            with self.assertRaises(ModuleNotFoundError):
+                util.import_('not_here')
+
     def test_name_requires_rparition(self):
         # Raise TypeError if a non-string is passed in for the module name.
         with self.assertRaises(TypeError):