title: How to display NULL value as unchecked state in a TDBCheckBox descendant?
body: <p>Having a nullable dataset field of a boolean type, how to display its <code>NULL</code> value as an unchecked state in a <code>TDBCheckBox</code> control descendant linked to this field. By default, <code>TDBCheckBox</code> displays the <code>NULL</code> value of the field as a grayed check box:</p>
  
  <p><img src="https://i.stack.imgur.com/YJsDK.png" alt="enter image description here"></p>
  
  <p>but I need it to be displayed as an unchecked state in my <code>TDBCheckBox</code> control descendant:</p>
  
  <p><img src="https://i.stack.imgur.com/XwabN.png" alt="enter image description here"></p>
  
  <p>Modifying the original <code>TDBCheckBox</code> source code is not an option for me, nor I cannot override the <code>TDBCheckBox.GetFieldState</code> because it's a private method.</p>
  
  <p>So, how can I display the <code>NULL</code> value as an unchecked state in my <code>TDBCheckBox</code> descendant ?</p>