title: Flame 0.29.4 cannot run with sound null safety
body: <p>When trying to run my Flame application I get the following error:</p>
  <blockquote>
  <p>Error: Cannot run with sound null safety, because the following
  dependencies don't support null safety:</p>
  <ul>
  <li>package:flame</li>
  <li>package:ordered_set</li>
  <li>package:box2d_flame</li>
  </ul>
  </blockquote>
  <p>I have the following in my <code>pubspec.yaml</code> file:</p>
  <pre class="lang-yaml prettyprint-override"><code>dependencies:
    flame: ^0.29.4
    flame_box2d: ^0.0.1
  </code></pre>