Is there a Linq method to add a single item to an IEnumerable?

Question

Basically I am trying to do something like this:

image.Layers

which returns an IEnumerable for all layers except the Parent layer,

Answer 1

/// 
Concatenates elements to a sequence.
/// The type of the elements of the input sequences.
/// The sequence to concatenate.
/// The items to concatenate to the sequence.
public static IEnumerable ConcatItems(this IEnumerable target, params T[] items)
{
    if (items == null)
        items = new [] { default(T) };
    return target.Concat(items);
}

This solution is based on realbart's answer. I adjusted it to allow the use of a single null value as a parameter:

var newCollection = collection.ConcatItems(null)