avoid recompilation if null environment key

Hi,
I'm using your library on my project. I did one small change on environmentsAllowRunning to avoid a NPE.

With this change, I can set the onlyRunWhenKey and onlyRunWhenValue, and the filter still works even if there is not any environment variable.

I did some more changes on the pom.xml that I don't think should be merged. I just don't know how to exclude those changes on github. :) If I have to change any thing on it, please let me know.