code: private List<Enum> getSelectableEnumsList(FormModel formModel,
  			String formPropertyPath, Map context) {
  		List<Enum> out = new ArrayList<Enum>();
  		Boolean nullable;
  		if (context.containsKey(NULLABLE_KEY)) {
  			nullable = (Boolean) context.get(NULLABLE_KEY);
  		} else {
  			nullable = this.nullable;
  		}
  		if (nullable) {
  			out.add(null);
  		}
  		for (Enum e : ((Class<Enum>) getPropertyType(formModel,
  				formPropertyPath)).getEnumConstants()) {
  			out.add(e);
  		}
  		return out;
  	}
docs: Adds the <code>null</code> value if this binder is nullable.