diff --git a/docker/models/containers.py b/docker/models/containers.py
index 4725d6f6f..536ac1af8 100644
--- a/docker/models/containers.py
+++ b/docker/models/containers.py
@@ -211,6 +211,8 @@ def exec_run(self, cmd, stdout=True, stderr=True, stdin=False, tty=False,
             resp['Id'], detach=detach, tty=tty, stream=stream, socket=socket,
             demux=demux
         )
+
+        exec_output = tuple(b'' if x is None else x for x in exec_output)
         if socket or stream:
             return ExecResult(None, exec_output)