Possible Null Reference Exception using "as" operator

Question

In the following code:

MyObject objInstance;

private void someEventHandler(object sender, EventArgs e)
{
    if (sender == objInstance && (sender as MyObject).SomeBoolProperty)
        // Do Something
}

Resharper is warning that sender as MyObject may be a possible NullReferenceException. Is that possible given this code? I'm assuming that if sender == objInstance that (sender as MyObject) won't return null, but this wouldn't be the first time a Resharper message has informed me of a C# behavior/feature I was unaware of.

Answer 1

When you use as, null is returned if the object couldn't be converted (in this case, to MyObject). Therefore, your line (sender as MyObject) has the potential to be null.