Quick fix

Author: kyb3r

core/thread.py

@@ -92,7 +92,7 @@ async def close(self, *, closer, after=0, silent=False, delete_channel=True, mes
         em.description = message or f'{closer.mention} has closed this modmail thread.'
         em.color = discord.Color.red()
 
-        if not silent:
+        if not silent and self.recipient is not None:
             tasks.append(self.recipient.send(embed=em))
 
         if delete_channel: