Thrown to indicate that an argument was null and should not have been. This exception supplements the standard IllegalArgumentException by providing a more semantically rich description of the problem.

NullArgumentException represents the case where a method takes in a parameter that must not be null. Some coding standards would use NullPointerException for this case, others will use IllegalArgumentException. Thus this exception would be used in place of IllegalArgumentException, yet it still extends it.

 public void foo(String str) {
   if (str == null) {
     throw new NullArgumentException("str");
   }
   // do something with the string
 }