Avoid using static access to Exception

The idea behind this warning is that if you embed the class names inside your code with the new keyword it will be hard to swap out these classes in testing and mock or stub methods that the code under test might call on them. See the explanation in the PHPMD rules.

I think in your case this is false positive since exceptions usually doesn't have much behavior on their own but the class name (and class hierarchy behind it) of them is pretty much the only thing important about them.

If you want to get rid of the warning here, you can use the @SupressWarnings annotation here.

Ahh, after a bit of digging around I have found the answer, straight from the horse's mouth.

In the configuration files, located at yourphpdir\data\PHP_PMD\resources\rulesets, the cleancode.xml has CDATA comments which explain the setting.

This one says:

Static acccess causes inexchangable dependencies to other classes and leads to hard to test code. Avoid using static access at all costs and instead inject dependencies through the constructor. The only case when static access is acceptable is when used for factory methods.

The way to solve it is just pass the exception as a parameter, so it's declared outside of the class.

$foo->setLang("Oh noes!", new InvalidArgumentException("No lang for you."));