Dealing with 204 status code

Hi,
I am getting data from an external database using ajax and works fine except when I get 204 code status. I would like to implement an if statement which shows an alert if the status code is 204 and show the data otherwise. I tried what has been suggested below, but I could not find a solution:
- https://datatables.net/forums/discussion/48805/ajax-204-nocontent-with-no-json-in-the-response-will-fire-the-ajax-error-handler
- https://datatables.net/forums/discussion/comment/117027/#Comment_117027

Here the code I have now:

table1 = $('#TraCountHeDaily1Table').DataTable({
                    "language": {
                        "loadingRecords": "No data available"
                        },
                    "ajax": {
                        "type":"GET",
                        "dataType":'json',
                        "url":'https://webtris.highwaysengland.co.uk/api/v1.0/reports/Daily?sites='+siteid+'&start_date='+dateFromDef+'&end_date='+dateToDef+'&page=1&page_size=40000&reportSubTypeId=0', 
                        "dataSrc": function (json) {
                        console.log(json);
                        return json.Rows;
                        }
                    },
                    "columns": [
                        { "data": "Report Date" },
                        { "data": "Time Period Ending" },
                        { "data": "Time Interval" },
                        { "data": "0 - 520 cm" },
                        { "data": "521 - 660 cm" },
                        { "data": "661 - 1160 cm" },
                    ],
                    columnDefs:[
                        {targets:0, "type": "date", "render": function(data, type) {
                        return type === 'sort' ? data : moment(data).format('L');
                        }
                        }
                    ]
                    });        

I am want to implement something like the code below, but it does not work:

"dataSrc": function (json) {
                if(json == {}) {      //empty json response
               alert('No data has been found')
               } else {
               return json.Rows;
               }
     }

Many thanks.
Alberto.