If you are a Java developer, you have handled issues with Java for a long time. The most often problem in the Java world is the NullPointerException.
Nullity is a natural consequence of reference types. If there is a reference, it has to refer to some object - or be null. If there is no this option, all the variable was initialized with some non-null expression - and even then, you'd have issues if variables were read during the initialization phase.