diff --git a/connexion/app.py b/connexion/app.py
index 38558b13b..76982ef46 100644
--- a/connexion/app.py
+++ b/connexion/app.py
@@ -68,6 +68,7 @@ def add_api(self, swagger_file: pathlib.Path, base_path: str=None, arguments: di
         """
         logger.debug('Adding API: %s', swagger_file)
         # TODO test if base_url starts with an / (if not none)
+        arguments = arguments or dict()
         arguments = dict(self.arguments, **arguments)  # copy global arguments and update with api specfic
         yaml_path = self.specification_dir / swagger_file
         api = connexion.api.Api(yaml_path, base_path, arguments)