c# 对象引用未设置为对象的实例（堆栈跟踪中未提及空引用）

Question

在发布模式下运行宁我的 windows 服务时，我收到 "Object reference not set to an instance of an object" 错误（请注意，正如您从我的堆栈跟踪中看到的那样，它没有提到与 NullReference 有关的任何事情都让我更加困惑）。每次我运行在调试模式下，代码工作得很好，但是一旦我构建它以在服务器上发布并启动它，它就会失败并出现对象引用错误。请参阅下面的堆栈跟踪，然后在下面查看我的代码；

=================================================================================

Error Message: [EventQueueBulkProcessingHandler] Failed to process events
Stack Trace: 

Error Message (INNER EXCEPTION LEVEL 1): Object reference not set to an instance of an object.
Stack Trace (INNER EXCEPTION LEVEL 1):
   at Voicebox.EventTriggers.Processing.Preparation.EventContactsFilter.Filter(ContactsModel contacts, ContactsFilterModel contactsFilterModel, Int32 clientId) in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Processing\Preparation\EventContactsFilter.cs:line 24
   at Voicebox.EventTriggers.Processing.Preparation.TriggerActionDetailsBuilder.CreateTriggerActionDetails(Trigger trigger, ITriggerEvent triggerEvent) in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Processing\Preparation\TriggerActionDetailsBuilder.cs:line 48
   at Voicebox.EventTriggers.Processing.Handlers.UserEventsHandler.<>c__DisplayClass6_0.<MapEventsToTriggers>b__0(Trigger t, ITriggerEvent e) in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Processing\Handlers\UserEventsHandler.cs:line 62
   at Voicebox.EventTriggers.Helpers.PermutationsHelper.<>c__DisplayClass0_1`3.<Permutations>b__1(TB b) in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Helpers\PermutationsHelper.cs:line 11
   at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
   at System.Linq.Enumerable.<SelectManyIterator>d__17`2.MoveNext()
   at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
   at System.Linq.Enumerable.<SelectManyIterator>d__17`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Voicebox.EventTriggers.Processing.Handlers.UserEventsHandler.<HandleAsync>d__5.MoveNext() in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Processing\Handlers\UserEventsHandler.cs:line 37
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Voicebox.EventTriggers.Processing.EventQueueBulkProcessingHandler.<ProcessEventsGrouppedByClient>d__8.MoveNext() in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Processing\EventQueueBulkProcessingHandler.cs:line 107
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Voicebox.EventTriggers.Processing.EventQueueBulkProcessingHandler.<ProcessInternal>d__6.MoveNext() in D:\Websites\VoiceboxTest\Voicebox\VoiceBox.EventTriggers\Processing\EventQueueBulkProcessingHandler.cs:line 52

=================================================================================

所以离开上面的堆栈跟踪，它说问题出在文件 EventContactsFilter 的第 24 行。这对我来说毫无意义，因为这是列表的初始化。见下面的代码；

            // this is the line 24 which the stack trace points too
            List<string> filterExpressions = new List<string>();

            foreach (var model in contactsFilterModel.Criteria)
            {
                string fieldName = GetFieldName(contacts.ListId, model.FieldID, clientId);

                FieldType fieldType = GetFieldType(model);
                FilterExpression FilterExpression = ExpressionBuilder.GetFilterExpression(fieldName, model, fieldType);
                var expression = FilterExpression.sqlExpression;
                filterExpressions.Add(expression);
            }

如您所见，错误是在创建新列表时抛出的，经过许多小时或在网上搜索后，我无法找出可能导致此问题的原因。如果有人能够提供帮助，我将永远欠你的债！！

Answer 1

我不太确定问题出在 List<string> 声明上。请在该声明周围使用 try-catch，并查看实际的错误消息是什么。

我的直觉告诉我问题不存在。也许在那条线之上或之下。我的猜测是foreach。无论哪种方式，try-catch 该代码 :)

c# 对象引用未设置为对象的实例（堆栈跟踪中未提及空引用）

c# object reference not set to an instance of an object (no mention of null reference in stack trace)

c#

model-view-controller

asp.net-mvc

windows-services