public FEELFnResult<String> invoke(@ParameterName("string") String string, @ParameterName("start position") Number start) {
        return invoke(string, start, null);
    }
@Test
    void invokeNull2ParamsMethod() {
        FunctionTestUtil.assertResultError(substringFunction.invoke((String) null, null), InvalidParametersEvent.class);
        FunctionTestUtil.assertResultError(substringFunction.invoke("test", null), InvalidParametersEvent.class);
        FunctionTestUtil.assertResultError(substringFunction.invoke(null, 0), InvalidParametersEvent.class);
    }