. </li>    <li>The operators with a nullable return type ignore any null input values, and return null if the input sequence is empty or contains only null values. If non-null values are present, the return value will be non-null. </li> </ul>  <p>It all sounds pretty simple, doesn&#39;t it? We just sum the numbers, and divide by the count. It&#39;s not <em>too</em> complicated, but we have a couple of things to consider:</p>  <ul>   <li>How should we count items - which data type should we use? Do we need t