Error in Process screen when attaching report to email

We have a requirement to attach custom report to email as an attachment. As per our requirement we created a process screen for this. Issue we are facing is, when we use below line of code we are getting “OBJECT REFERENCE ERRO”, can you please have a look at below sample code.

 public class ProcessReports : PXGraph<ProcessReports>
    {
        [InjectDependency]
        protected IReportLoaderService ReportLoader { get; private set; }

        [InjectDependency]
        protected IReportRenderer ReportRenderer { get; private set; }

        public PXCancel<DACName> Cancel;

        public PXProcessing<DACName, Where<DACName.DACName, Equal<OPR>>> QueueList;
        public ProcessReports()
        {
            QueueList.SetProcessDelegate(delegate (List<DACName> list)
            {
                SaveFile(list, true);
            });
        }

        public static void SaveFile(List<DACName> list, bool aIsMassProcess)
        {
            new KWProcessWorkCenterOpenJobReports().save(list, aIsMassProcess);
        }
        public virtual void save(List<DACName> list, bool aIsMassProcess)
        {
            //here at this point we are getting error
            Report _report = ReportLoader.LoadReport("AA501108", null);
        }
    }