title: toString if condition is true add something
body: <p>Well I have this ToString method:</p>
  <pre><code>public override string ToString() =&gt; $&quot;{id} {Lastname} {Firstname} [{IsMale} {done}]&quot;;
  </code></pre>
  <p>And if Done is not null between IsMale and Done should be a <code>,</code> but if the Done is null there should be nothing</p>