specify default user_directory_include_pattern

synapse/config/user_directory.py

@@ -22,6 +22,7 @@ class UserDirectoryConfig(Config):
     """
 
     def read_config(self, config):
+        self.user_directory_include_pattern = None
         user_directory_config = config.get("user_directory", None)
         if user_directory_config:
             self.user_directory_include_pattern = (