PhpStorm - best PHP IDE has debugger method.
For your understanding. Debugger in PHP not traditional debugger such JS, JAVA, C++, Assembler, SoftIce for windows, and other.
Usually for null PHP soft debugger no need :)
How to "null" it is hack question. In all cases using different methods.
For example modules for Prestashop on this forum. First case I use a patch in code, other case proxy patch to intercept module requests.
Sometime nulled is impossible. For example module which use with mobile APP...