Nulls Brawl APK is a private server version of Brawl Stars. A private server means it is not connected to the official Supercell servers. Instead, it runs on its own independent system. This allows developers to modify the game and give players special features.However, because Nulls Brawl APK is not official, you cannot use your real Brawl Stars account. You need to create a new account inside the private server. Your progress will stay only in the Nulls Brawl server.