When to check for null arguments and throw ArgumentNullException
<p>I have some code like this:</p>

<pre><code>public void someMethod (Object x)
{
   if (x == null) throw new ArgumentNullException ();

   // more code...
}
</code></pre>

<p>Should I now do this:</p>

<pre><code>public void myMethod (Object z)
{
    someMethod (z);
}
</code></pre>

<p>Or this:</p>

<pre><code>public void myMethod (Object z)
{
    if (z == null) throw new ArgumentNullException ();

    someMethod (z);
}
</code></pre>

<p>Note: I prefer speed of execution in this class</p>
