验证模型属性但允许空值

Question

我试图让模型属性验证起作用，但在字符串属性中允许空值。

我试图验证的财产是：

public string PhoneNumber { get; set;}

我正在验证这个：

[Phone(ErrorMessage = "Invalid telephone number.")]
public string PhoneNumber { get; set;}

除了没有为电话号码发送值到带有对象的api时，验证在我的情况下效果很好。

有没有像：[AllowNullValue]属性或者我如何获得空值传递＆＃34;电话＆＃34;属性？

更新（Anton Gorbunov的帖子）：

{
    "Message": "An error has occurred.",
    "ExceptionMessage": "The  field is not a valid phone number.",
    "ExceptionType": "System.ComponentModel.DataAnnotations.ValidationException",
    "StackTrace": "   at System.ComponentModel.DataAnnotations.ValidationAttribute.Validate(Object value, String name)\r\n   at RABE_BCV_API.Controllers.APIController.UpsertMember(MemberModel memberObject) in C:\\Users\\John\\Documents\\Visual Studio 2015\\Projects\\RABE_BCV_API\\RABE_BCV_API\\Controllers\\APIController.cs:line 29\r\n   at lambda_method(Closure , Object , Object[] )\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"
}