code: protected Object doSetValue( String name,
                                   Object value ) {
          if (value == null) {
              value = Null.getInstance();
          } else {
              value = Utility.unwrap(value);
          }
          return document.put(name, value);
      }
docs: The method that does the actual setting for all of the <code>set...</code> methods. This method may be overridden by
  subclasses when additional work needs to be performed during the set operations.
  
  @param name the name of the field being set
  @param value the new value
  @return the old value, or null if there was no existing value