public FEELFnResult<String> invoke(@ParameterName("from") Object val) {
        if ( val == null ) {
            return FEELFnResult.ofResult( null );
        } else {
            return FEELFnResult.ofResult( TypeUtil.formatValue(val, false) );
        }
    }
@Test
    void invokeContextNonEmpty() {
        final Map<String, Object> childContextMap = new HashMap<>();
        childContextMap.put("childKey1", "childValue1");

        final Map<String, Object> contextMap = new HashMap<>();
        contextMap.put("key1", "value1");
        contextMap.put("key2", childContextMap);

        FunctionTestUtil.assertResult(stringFunction.invoke(contextMap), "{ key1 : value1, key2 : { childKey1 : " +
                "childValue1 } }");
    }