diff --git a/openapi_core/contrib/aiohttp/responses.py b/openapi_core/contrib/aiohttp/responses.py
index 547ebe62..40771e2f 100644
--- a/openapi_core/contrib/aiohttp/responses.py
+++ b/openapi_core/contrib/aiohttp/responses.py
@@ -14,6 +14,8 @@ def __init__(self, response: web.Response):
 
     @property
     def data(self) -> str:
+        if self.response.body is None:
+            return ""
         if isinstance(self.response.body, bytes):
             return self.response.body.decode("utf-8")
         assert isinstance(self.response.body, str)