Update SessionHandler.php

[ChrisWeller]

If there is no session on reading the result was returned as null, it now returns an empty string which PHP (7.1) handles without error.

[andersonbuzzi]

You read my thoughts. I got this error here and this fix it. Tks.,

[programster]

Thank you for raising this issue and submitting a merge request. I'm a bit confused about the problem:

If there is no session on reading the result was returned as null, it now returns an empty string which PHP (7.1) handles without error.

Are we saying that the code does have a session because it has timed out, just before the call to getting session data or something? Or are we saying that the application has never called session_start() before trying to read a session variable?
A short piece of code I could run to demonstrate the issue would be great (if possible).

[programster]

Please can you fix this so that we have the original indentation using 4 spaces. This way the actual/real changes are easy to see/view.