title: Unity nullable integer as a inspector field
body: <p>I created a <code>Serializable</code> class for my inspector.</p>
  
  <pre><code>[Serializable]
  public class CellType
  {
      [SerializeField]
      public int? Cost; // This does not appear in the inspector
  
      [SerializeField]
      public Color MaterialColor;
  }
  </code></pre>
  
  <p>The nullable field <code>Cost</code> does not appear in the inspector. I use this class by creating a <code>SerializeField</code></p>
  
  <pre><code>[SerializeField]
  private CellType[] types;
  </code></pre>
  
  <p>If the field <code>Cost</code> would be a default int the field would appear. Is a workaround possible?</p>