While using the for loop to print messages, this error comes up. --------------------------------------------------------------------------- TypeError Traceback (most recent call last) [<ipython-input-38-35622cd23eff>](https://localhost:8080/#) in <cell line: 1>() 6 print("Preview: " + message.snippet) 7 ----> 8 print("Message Body: " + message.plain) # or message.html TypeError: can only concatenate str (not "NoneType") to str