diff --git a/lib/matplotlib/backends/backend_webagg_core.py b/lib/matplotlib/backends/backend_webagg_core.py
index 37ce69c59103..4c1b0a0f57cd 100644
--- a/lib/matplotlib/backends/backend_webagg_core.py
+++ b/lib/matplotlib/backends/backend_webagg_core.py
@@ -236,8 +236,7 @@ def get_diff_image(self):
                 self._last_renderer, renderer)
             self._force_full = False
             self._png_is_old = False
-
-        return buff
+            return buff
 
     def get_renderer(self, cleared=None):
         # Mirrors super.get_renderer, but caches the old one
@@ -487,8 +486,9 @@ def handle_json(self, content):
     def refresh_all(self):
         if self.web_sockets:
             diff = self.canvas.get_diff_image()
-            for s in self.web_sockets:
-                s.send_binary(diff)
+            if diff is not None:
+                for s in self.web_sockets:
+                    s.send_binary(diff)
 
     @classmethod
     def get_javascript(cls, stream=None):