Data column(s) for axis #0 cannot be of type string× in google bar chart when number of row =0 selected from database

Question

I'm using the following code to create a JSON string from data extracted from a database:

var jsonData = $.ajax({
        url: "pie_chart.php",
        dataType:"json",
        method:"POST",
        data:$('#myform').serialize(),
        async: false,
        success: function(jsonData)
        {
        console.log(jsonData);
        var data =  google.visualization.arrayToDataTable(jsonData);