Add support for PHP 7.4

[slt]

Summary

PHP 7.4 deprecates curly brace syntax $s{0} in favour of using regular array syntax $s[0]

Fix null array issue

Checklist

• [/] Added changelog entry
• [/] Ran unit tests (Check the README for instructions)

[crookedneighbor]

Thanks, this will go out in our next release.

[crookedneighbor]

Sorry for the delay. This is out in 4.6.0