I'm executing RecordService.Instance.Approve(record, form) asynchronously to update the status to approved but I'm getting the following error:

System.ArgumentNullException (umbraco)
             ...      Value cannot be null.
             ...      Parameter name: umbracoContext
             ...         at Umbraco.Web.Security.MembershipHelper..ctor(UmbracoContext umbracoContext, MembershipProvider membershipProvider, RoleProvider roleProvider)
             ...         at Umbraco.Forms.Data.StringHelper.ParsePlaceHolders(HttpContext context, Record record, String value)
             ...         at Umbraco.Forms.Data.StringHelper.ParsePlaceHolders(Record record, String value)
             ...         at Umbraco.Forms.Core.Services.WorkflowService.ExecuteWorkflows(List`1 workflows, RecordEventArgs e)
             ...         at Umbraco.Forms.Core.Services.WorkflowService.ExecuteWorkflows(Record record, Form form, FormState state, Boolean editMode)
             ...         at Umbraco.Forms.Web.Services.RecordService.Approve(Record record, Form form)

Did anyone here encountered the same error?

Here are my code:

var task = new System.Threading.Tasks.Task(() =>
                            {
                                    if (formRecord != null)
                                    {
                                        Umbraco.Forms.Core.Record record = GetRecordByUniqueID(formRecord.UniqueId);
                                        if (record != null)
                                        {


                                            #region Update Record Status
                                            try
                                            {
                                                //Update form record status to approved 
                                                using (var formStorage = new Umbraco.Forms.Data.Storage.FormStorage())
                                                {
                                                    Umbraco.Forms.Core.Form form = formStorage.GetForm(record.Form);

                                                    if (record.RecordFields.Any(x => x.Value.Field.Caption == "Payment Reference"))
                                                    {
                                                        record.GetRecordField("Payment Reference").Values.Clear();
                                                        record.GetRecordField("Payment Reference").Values = new List<object> { tranid };
                                                    }
                                                    RecordService.Instance.Approve(record, form); 

                                                }
                                            }
                                            catch (Exception ex)
                                            {

                                            }
                                            #endregion
                                        }
                                    }


                            });
                            task.Start();