title: How can the type of a bean property be null?
body: <p>In the book "Thinking in Java" there is an example of how to get information for a bean via Reflection/Introspection.</p>
  
  <pre><code>BeanInfo bi = Introspector.getBeanInfo(Car.class, Object.class);
  for (PropertyDescriptor d: bi.getPropertyDescriptors()) {
    Class&lt;?&gt; p = d.getPropertyType();
    if (p == null) continue;
    [...]
  }
  </code></pre>
  
  <p>In line 4 of that sample above there is a check if the PropertyType is null. When and under what circumstances does that happen? Can you give an example?</p>