ajax - ajaxでアクセスするとjsonがundefinedを返す

Question

json オブジェクトを返すコントローラーがあります。コントローラーをチェックしたところ、正常に動作しています。

これが私のコントローラーのサンプル結果です

{"CompliantCount":0,"NonCompliantCount":0,"StatusOfRiskItems":[{"Id":4,"Status":"Closed","Count":0},{"Id":1,"Status":"Open","Count":0},{"Id":2,"Status":"Mitigating Control Implemented","Count":0},{"Id":3,"Status":"Risk Accepted","Count":0}],"RiskLevelBreakdownOfOpenItems":[{"Id":0,"RiskLevel":"N/A","Count":0},{"Id":1,"RiskLevel":"Low","Count":0},{"Id":2,"RiskLevel":"Medium","Count":0},{"Id":3,"RiskLevel":"High","Count":0},{"Id":4,"RiskLevel":"Very High","Count":0}],"RiskLevelStatusPerDepartment":[],"CompliancePerDepartment":[],"CurrentRiskLevel":"N/A","ComplianceRating":NaN}

しかし、ajax で json を使用すると、null が返されます

function RiskRegisterReport(siteId, programId, departmentId, status, auditType, auditor, auditDate) {
  var _data;
  $.ajax({
    type: "GET",
    contentType: "application/json; charset=utf-8;",
    url: hostpath + "/RiskRegister/RiskRegisterReport/",
    dataType: "json",
    async: false,
    data: {
        siteId: siteId,
        programId: programId,
        departmentId: departmentId,
        statusId: status,
        auditType: auditType,
        auditor: auditor,
        auditDate: auditDate
    },
    success: function (data) {
        /// after getting the data
        /// push  the data.Compliant and data.NonCompiant to the array
        _data = data;
    }
  });
  return _data;
}