auto-converting non-lists to list values.

src/server/BreCal/validators/validation_error.py

@@ -25,6 +25,7 @@ def create_validation_error_response(ex:ValidationError, status_code:int=400)->t
     # the following conversion snipped ensures a dictionary output
     if isinstance(errors, (str,list)):
         errors = {"undefined_schema":errors}
+    errors = {k:v if isinstance(v,list) else [v] for k,v in errors.items()}
 
     # hence, errors always has the following type: dict[str, list[str]]