; <span class="Statement">throw</span>&#160;<span class="Keyword">new</span> ArgumentNullException(<span class="String">&quot;source&quot;</span>);     <br />&#160;&#160;&#160; }     <br />&#160;&#160;&#160; <span class="Statement">checked</span>     <br />&#160;&#160;&#160; {     <br />&#160;&#160;&#160;&#160;&#160;&#160;&#160; <span class="ValueType">long</span> count = 0;     <br />&#160;&#160;&#160;&#160;&#160;&#160;&#160; <span class="ValueType">long</span> total = 0;     <br />&#160;&#160;&#160;&#160;