json and empty array

I have the following json :

{
   "users":
    [{
       "user": 
        {
        "user_id"  :"a11uhk22hsd3jbskj",
        "username" :"tom",
        "location" : null
        }
    }]
}

I get this json in response to a request to an api. Looking at the doc for this api, location is supposed to be an array (containing geodata, latitude, longitude address etc).
Now the question is : there's an error in the json? I mean, location doesn't seems,to me, to be an array, or is possible to represent a null array in that way? and if yes what is the difference between :

"location" : null 
"location" : []