An object reference from local assignment of a null-constant or from a call to a function that will return null will be passed to a function that can dereference it, without checking for null.

Vulnerability and risk

Dereferencing a null object reference is a critical runtime problem that will crash the application on some operating systems and throw a runtime exception on others.

Example 1

1  public class A {
2    public void abc() {}
3     public void foo(A a) {
4      if (flag)
5        return;
6      a.abc();
7     }
8  
9     public void var() {
10     A a = null;
11     foo(a);
12    }
13 
14    private bool flag;
15 }

Klocwork produces an issue report (CS.NRE.GEN.CALL.MUST) at line 11 for variable 'a'. Variable 'a' is explicitly assigned to null value at line 10 and will be passed as argument 1 to function 'foo' at line 11, which may dereference it.