diff --git a/girder/api/describe.py b/girder/api/describe.py
index <HASH>..<HASH> 100644
--- a/girder/api/describe.py
+++ b/girder/api/describe.py
@@ -629,6 +629,8 @@ class autoDescribeRoute(describeRoute):  # noqa: class name
             params = {k: v for k, v in six.viewitems(kwargs) if k != 'params'}
             params.update(kwargs.get('params', {}))
 
+            kwargs['params'] = kwargs.get('params', {})
+
             for descParam in self.description.params:
                 # We need either a type or a schema ( for message body )
                 if 'type' not in descParam and 'schema' not in descParam:
Fix __call__: create 'params' in kwargs if needed

This function call the _passArgs which assumes the params is a valid
dictionary in kwargs.