Question

In my REST WCF service I log all exceptions on WCF stack level (IErrorHandler)

Here is my code:

public void PostPositions(List<Position> positions)
{
    if (!this.ValidateRequest()) return;
    foreach (var position in positions)
    {

I get exception:

Object reference not set to an instance of an object.

at Web.Services.MobileService.PostPositions(List`1 positions)
in
C:\CodeWorkspace\ClientServerCode\Web.Services\Rest\MobileService.cs:line
1170 at SyncInvokePostPositions(Object , Object[] , Object[] )
at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object
instance, Object[] inputs, Object[]& outputs)

Line 1170 in my code is for if (!this.ValidateRequest()) return;

What does it mean? There is no static methods, I work with instance of a class and this definitely exists. If exception happens inside ValidateRequest() I expect stack trace to show that.

Any pointers?

Answer 1

I would be willing to bet that positions is what’s null and that foreach(var position in positions) is what’s throwing the exception when calling GetEnumerator() on positions.

if(positions != null)
{
    foreach(var position in positions)
    {
        ...
    }
}

As you might guess, it’d be very easy for the line number calculation to get a bit jumbled here, since the foreach loop is just syntactic sugar for something like this:

IEnumerator<Position> enumerator = positions.GetEnumerator();

try
{
    Position position;

    while(enumerator.MoveNext())
    {
        position = enumerator.Current;

        //The code from the body of your foreach loop goes here
    }
 }
 finally
 {
     //Clean up the enumerator
 }