Thrown when an application attempts to use <code>null</code> in a case where an object is required. These include: <ul> <li>Calling the instance method of a <code>null</code> object. <li>Accessing or modifying the field of a <code>null</code> object. <li>Taking the length of <code>null</code> as if it were an array. <li>Accessing or modifying the slots of <code>null</code> as if it were an array. <li>Throwing <code>null</code> as if it were a <code>Throwable</code> value. </ul> <p> Applications should throw instances of this class to indicate other illegal uses of the <code>null</code> object.