Fix zero as null pointer constant warning

[MartinDelille]

This PR simply replace 0 or NULL by nullptr. It allow compiling the code with the following compiler flags:

-Werror -Wzero-as-null-pointer-constant

[MartinDelille]

Ok it fails because I made my modification from the version tagged by the current https://github.com/banditcpp/bandit master branch.

What do you prefer me to do?

• Push a new PR against the currrent master branch?
• Create a PR against another branch?

[MartinDelille]

Ok I repushed my commit against the current master branch.

[sbeyer]

Thank you very much.

Yes, please always use the master branch for changes. Please amend your commit, so that I can merge. I will then update the headers-only branch which is used by bandit, and you can then update your bandit PR.