In the context of Dolibarr and other web software, a "nulled" module is a paid add-on that has been hacked or modified to bypass its licensing verification. Essentially, pirates remove the code that checks if the user has purchased a valid license key, allowing anyone to download and install the module without paying the developer.
On the surface, this seems like a boon for startups or businesses on a tight budget. Why pay €100 or €500 for a module when you can find a "Nulled" version for free?
