[2.8.0, 2.9.0] Aggregation function attempted to calculate value using empty array

[anatoly-spb]

Hello!

I have a simple json:

{
 "array": [
   {
    "count": 1
   },
   {
    "count": 2
   },
   {
    "count": 3
   }
 ]
}

Is it possible to use aggregate in the following case:

	@Autowired
	com.jayway.jsonpath.Configuration jsonPathConfiguration;
	
	@Test
	void parseJson() {
	  Object object = jsonPathConfiguration.jsonProvider().parse("{\n"
	      + "      \"array\": [ \n"
	      + "       {\n"
	      + "           \"count\": 1\n"
	      + "       },\n"
	      + "       {\n"
	      + "           \"count\": 2\n"
	      + "       },\n"
	      + "       {\n"
	      + "           \"count\": 3\n"
	      + "       }\n"
	      + "       ]\n"
	      + "   }");
	  assertThat(object).isNotNull().isInstanceOf(Map.class);
	  JsonPath countSum = JsonPath.compile("$.array[*].count.sum()");
	  countSum.read(object);
	}

?

Now I got the exception:

com.jayway.jsonpath.JsonPathException: Aggregation function attempted to calculate value using empty array
	at com.jayway.jsonpath.internal.function.numeric.AbstractAggregation.invoke(AbstractAggregation.java:59)
	at com.jayway.jsonpath.internal.path.FunctionPathToken.evaluate(FunctionPathToken.java:41)
	at com.jayway.jsonpath.internal.path.PathToken.handleObjectProperty(PathToken.java:90)
	at com.jayway.jsonpath.internal.path.PropertyPathToken.evaluate(PropertyPathToken.java:80)
	at com.jayway.jsonpath.internal.path.PathToken.handleArrayIndex(PathToken.java:143)
	at com.jayway.jsonpath.internal.path.WildcardPathToken.evaluate(WildcardPathToken.java:42)
	at com.jayway.jsonpath.internal.path.PathToken.handleObjectProperty(PathToken.java:90)
	at com.jayway.jsonpath.internal.path.PropertyPathToken.evaluate(PropertyPathToken.java:80)
	at com.jayway.jsonpath.internal.path.RootPathToken.evaluate(RootPathToken.java:66)
	at com.jayway.jsonpath.internal.path.CompiledPath.evaluate(CompiledPath.java:99)
	at com.jayway.jsonpath.internal.path.CompiledPath.evaluate(CompiledPath.java:107)
	at com.jayway.jsonpath.JsonPath.read(JsonPath.java:179)
	at com.jayway.jsonpath.JsonPath.read(JsonPath.java:153)

But there is a work around:

Object counts = JsonPath.read(object, "$.array[*].count");
Object countSum = JsonPath.read(counts, "$.sum()"); // 6.0(Double)