Inconsistent exception behavior in FirstOrDefault() method with lambda expressiion

[RobR]

Greetings!

I am working with the following code in MS Visual Studio 2008:

SimpleADONetField foundField = null;
foundField = fieldList.FirstOrDefault(field => field.m_name == checkedNode.Text);
if (foundField == null)
{
	SimpleADONetField tagField = (SimpleADONetField)checkedNode.Tag;
	fieldList.Add(tagField);
}

The first time this code is executed, the fieldList object exists but it is empty.

When I step through this code, it behaves as I expect. Since fieldList is empty, nothing can match the condition, and foundField is set to null, which is the default value for reference types. But if I run my application through the VS debugger without stopping in this code, it throws a null reference exception, complaining that the field object is null when I try to read its m_name property.

Why do I get an exception when running the code without stopping and not get an exception when stepping through it? Which behavior is correct? I can of course check to see if the list is empty before I run this code, but I don't think I should have to do that.

Thank you very much.

RobR