Can't get values from JSON array. [null object]

Hi. I'm trying to parse response as an array of arrays. 

For some reason "An error occurred [null object]"

[
      {
      "id": ,
      "number": ,
      "name": "some info",
      "description": "<p><\/p><p><br><\/p><p><span class=\"Apple-tab-span\" style=\"white-space:pre\">\t<\/span>Lorenzo<\/p>",
      "description_no_html": "sdgsgs",
      "state": "New",
      "priority": "Low",
},
{
...
}
]

My script is:

def category = "bla bla bla"

def ResponseMessage = testRunner.testCase.testSteps["Get all incidents from Samanage before termination"].testRequest.response.contentAsString
def jsonSlurper = new JsonSlurper().parseText(ResponseMessage)

def responseSize = jsonSlurper.size()
def terminations = []



def responseCategory
//Get all the terminations for specified date from response
for (int i=0;i<responseSize;i++){
	responseCategory = jsonSlurper[i].category.name.toString()
	if (responseCategory.equals(category))
	terminations << jsonSlurper[i].id
}

Can someone help me with that? The JSON is valid and in case if 

jsonSlurper[1].id

 i'll get correct value. But in FOR structure it's not working