Null pointer dereference occurs when application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Null pointer errors are usually the result of one or more programmer assumptions being violated. They will always result in the crash of the process, unless exception handling (on some platforms) is invoked, and even then, little can be done to salvage the process. Null-pointer dereference issues can occur through a number of flaws, including race conditions and simple programming omissions.”]
Source: https://owasp.org/www-community/vulnerabilities/Null_Dereference