Here is the explaination from JLS:
The following example demonstrates that a null reference may be used to access a class (static) variable without causing an exception:
class
Test {
static String mountain = "Chocorua";
static Test favorite(){
System.out.print("Mount ");
return null;
}
public static void main(String[] args) {
System.out.println(favorite().mountain);
}
}
It compiles, executes, and prints:
Mount Chocorua
Even though the result of favorite() is null, a NullPointerException is not thrown. That "Mount " is printed demonstrates that the Primary expression is indeed fully evaluated at run time, despite the fact that only its type, not its value, is used to determine which field to access (because the field mountain is static).