/span> source.Select(selector).Average();     <br />}     <br />    <br /><span class="Modifier">public</span>&#160;<span class="Modifier">static</span>&#160;<span class="ValueType">double</span>? Average(<span class="Keyword">this</span> IEnumerable&lt;<span class="ValueType">int</span>?&gt; source)     <br />{     <br />&#160;&#160;&#160; <span class="Statement">if</span> (source == <span class="Keyword">null</span>)     <br />&#160;&#160;&#160; {     <br />&#160;&#160;&#160;&#160;&#160;&#160;&#160; <span