code: protected JComponent createSelector(String fieldName, Constraint filter) {
  		Map context = new HashMap();
  		context.put(ComboBoxBinder.FILTER_KEY, filter);
  		return getBindingFactory().createBinding(JComboBox.class, fieldName).getControl();
  	}
docs: Creates a component which is used as a selector in the form. This
  implementation creates a {@link JComboBox}
  
  @param fieldName the name of the field for the selector
  @param filter an optional filter constraint
  @return the component to use for a selector, not null