对象引用未设置为Page Load上对象的实例

Question

这很模糊。所以任何帮助将不胜感激。但为什么我的'workPhase'变量不会被设置为对象的实例？我想不明白。这是我的代码：

   public WorkPhaseMultiCodingManageEdit.Command Handle(Query query)
                {  
    var workPhase = _db.WorkPhases.FirstOrDefault(x => x.Id == query.WorkPhaseIds.FirstOrDefault());        
                    var result = new WorkPhaseMultiCodingManageEdit.Command();        
                    result.WorkPhaseIds = query.WorkPhaseIds;
                    result.Job = workPhase.Job;
                    result.JobId = workPhase.JobId;
                    result.Disabled = !_authService.DoesUserHaveAccess(Feature.WBSConfigurationCodingSection);        
                    var codingFields = _codingFieldService.GetCodingFields(workPhase);
                    foreach (var codingFieldItem in codingFields)
                    {
                        var codingValuesForThisCodingField = _db.WorkPhases
                            .SelectMany(x => x.CodingFields)
                            .Where(x => query.WorkPhaseIds.Contains(x.WorkPhaseId))
                            .Where(x => x.CodingFieldValue.CodingFieldId == codingFieldItem.CodingFieldId)
                            .Select(x => x.CodingFieldValueId)
                            .ToList();        
                        if (codingValuesForThisCodingField.Distinct().Count() > 1 ||
                            (codingValuesForThisCodingField.Count > 0 && codingValuesForThisCodingField.Count != query.WorkPhaseIds.Count))
                        {
                            var options = new List<DropDownItem>() { new DropDownItem() { Id = -1, Name = "Various" } };
                            options.AddRange(codingFieldItem.Options);
                            codingFieldItem.Options = options;
                            codingFieldItem.CodingFieldValueId = -1;
                        }
                        else if (codingValuesForThisCodingField.Count() == query.WorkPhaseIds.Count)
                        {
                            codingFieldItem.CodingFieldValueId = codingValuesForThisCodingField.First();
                        }
                        else
                        {
                            codingFieldItem.CodingFieldValueId = 0;
                        }        
                        result.CodingFields.Add(codingFieldItem);
                    }    
                    return result;
                }
            }