Fixed an exception that occurs when parse_message_line receives empty string

[nitzanfarhi]

Hi 😄 ,
an exception occured to me when parse_message_line receives an empty string.
When this occurs, parse_message_line returns None.
After that, "\n".join throws an exception when one of the members of the list is none.

Example to an input that causes this is:

parts['message']='    Adding titles to links\n    \u2028\n'

The fix is simple, replace None with empty string.

[nitzanfarhi]

I will also add that this occurs in general when chars like \u2028 exist since they are considered as line breaks.