Raise ValueError on invalid parent

Signed-off-by: Filipe Laíns <lains@riseup.net>

Author: FFY00

Lib/importlib/_bootstrap_external.py

@@ -1327,6 +1327,8 @@ def find_spec(cls, fullname, path=None, target=None):
     def discover(cls, parent=None):
         if parent is None:
             path = sys.path
+        elif parent.submodule_search_locations is None:
+            raise ValueError(f'{parent} is not a package module')
         else:
             path = parent.submodule_search_locations