If you have the `--fixers` option, you can have 2 types: whitelist and blacklist.
If you are using the whitelist, you have to clear the fixers and add only the ones you want.
If you have the blacklist `--fixers=-psr0` you need to get all fixers and remove the ones you don't need.

The previous verification was clearing the array independent of which type of fixer you were using, therefore the command using `--fixers=-psr0` was not working.

I've copied the same if (lazy) used on line 210. I think it became a bit complicated to understand :/

I will remove the bang (!) and invert the null with the getFixers(), i think it will be easily understandable.