docs: protected Boolean _generate(XNullLiteral expression, XExpression parentExpression, XtendExecutable feature,
  			InlineAnnotationTreeAppendable output) {
  		if (parentExpression == null && feature instanceof XtendFunction) {
  			final XtendFunction function = (XtendFunction) feature;
  			output.append("("); //$NON-NLS-1$
  			final JvmTypeReference reference = getFunctionTypeReference(function);
  			if (reference != null) {
  				final JvmType type = reference.getType();
  				if (type != null) {
  					output.append(type);
  				} else {
  					output.append(Object.class);
  				}
  			} else {
  				output.append(Object.class);
  			}
  			output.append(")"); //$NON-NLS-1$
  			output.append(Objects.toString(null));
  			output.setConstant(true);
  		} else {
  			output.appendConstant(Objects.toString(null));
  		}
  		return Boolean.TRUE;
  	}