title: How to use built-in editors for a exposed properties in User Controls - Mask Property Editor Issue
body: <p>I think there is a simple solution for my stupid question but I just can't solve it today.</p>
  
  <p>I have a User Control that has a <code>MaskedTextBox</code> Control in itself. I have also exposed a few of its properties for the user to modify.</p>
  
  <p>One of these properties is <code>Mask</code> property which I want to expose with the ability of starting an editor with predefined values like in a normal MaskedTextBox control.</p>
  
  <p>So I created a public property InputMask and set up everything so that it can work but after showing the editor, I get an error dialog which contains this error:</p>
  
  <blockquote>
    <p>Object reference not set to an instance of an object</p>
  </blockquote>
  
  <p>If i don't use editor and copy a mask or set it trough code works without problems.</p>
  
  <p>Here is a code sample:</p>
  
  <pre><code>...
  MaskedTextBox maskedtextbox;
  myUserControl()
  {
      ...
      maskedtextbox = new MaskedTextBox(){
          some stuff...
      };
  }
  
  [DefaultValue("")]
  [Editor("System.Windows.Forms.Design.MaskPropertyEditor, System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", typeof(UITypeEditor))]
  [Localizable(true)]
  [MergableProperty(false)]
  [RefreshProperties(RefreshProperties.Repaint)]
  public string InputMask
  {
      get { return this.maskedtextbox.Mask; }
      set { this.maskedtextbox.Mask = value; }
  }
  </code></pre>