public FEELFnResult<List> invoke(@ParameterName( "list" ) Object list) {
        if ( list == null ) {
            return FEELFnResult.ofError(new InvalidParametersEvent(Severity.ERROR, "list", "cannot be null"));
        }
        // spec requires us to return a new list
        final List<Object> result = new ArrayList<>();
        flattenList( list, result );
        return FEELFnResult.ofResult( result );
    }
@Test
    void invokeParamNotCollection() {
        FunctionTestUtil.assertResult(flattenFunction.invoke(BigDecimal.valueOf(10.2)),
                                      Collections.singletonList(BigDecimal.valueOf(10.2)));
        FunctionTestUtil.assertResult(flattenFunction.invoke("test"), Collections.singletonList("test"));
    }