System.InvalidOperationException: Sequence contains no elements

foreach (var keyCode in unexpectedKeyCodesDetected)
{
　　string unexpected = expectedCapturedKeyCodes.Where(key => key == keyCode).First();
}

空集合时，从First（）处 Throw the exceptoins. 

修改:  First() => FirstOrDefault()，然后对返回String做null判断。