ArgumentNullException is thrown when a method is invoked and at least one of the passed arguments is null but should never be null.

ArgumentNullException behaves identically to ArgumentException. It is provided so that application code can differentiate between exceptions caused by null arguments and exceptions caused by arguments that are not null. For errors caused by arguments that are not null, see ArgumentOutOfRangeException.

ArgumentNullException uses the HRESULT E_POINTER, which has the value 0x80004003.

For a list of initial property values for an instance of ArgumentNullException, see the ArgumentNullException constructors.

The following example demonstrates an error that causes the string class to throw a ArgumentNullException exception.

using System;
class ArgumentNullTest {
 public static void Main() {
 String[] s = null;
 String sep = " ";
 try {
 String j = String.Join(sep,s);
 }
 catch (ArgumentNullException e) {
 Console.WriteLine("Error: {0}",e);
 }
 }
}
   

The output is