title: Error: Operator '[]' cannot be called on 'String?' because it is potentially null. }
body: <pre><code>main() {
      String? variable1=stdin.readLineSync();
      String? variable2=variable1[0]; // Error: Operator '[]' cannot be called on 'String?' because it is potentially null.
  }
  </code></pre>
  <p>Why do I need to add null check when <code>variable2</code> is already <code>null</code> safe?
  I know how to correct this, please explain why is this happening.</p>