falcon response data none fix

Author: p1c2u

openapi_core/contrib/falcon/responses.py

@@ -9,6 +9,8 @@ def __init__(self, response: Response):
 
     @property
     def data(self) -> str:
+        if self.response.text is None:
+            return ""
         assert isinstance(self.response.text, str)
         return self.response.text