Fix: Do not pass null to function that expects string

[localheinz]

This pull request

• stops passing null to a function that expects string

Follows php/web-php#850.

[kamil-tekiela]

I don't think this deprecation warning happens here. We use this on master and there are no warnings. If you diff the two files, you will see that the one in web-php is a much older version. What I proposed is that we just copy over the latest version from php-src into web-php. I don't think there is a need to change $php declaration here or there for that matter. Sorry for the confusion.