/// <summary>
/// If the given <paramref name="value"/> is not effective, the algorithm searches
/// for the first effective value in <paramref name="deflts"/>, otherwise the <paramref name="value"/> is returned.
/// </summary>
/// <returns><paramref name="value"/> if effective, otherwise the first effective value of
/// <paramref name="deflts"/> if exists, otherwise <c>null</c>.</returns>
/// <param name="value">The value to check and possible return.</param>
/// <param name="deflts">An list of default values that must be tried all until a non-effective
/// value is found, or the end of the list is reached.</param>
/// <typeparam name="T">The type of elements over which the function is defined.</typeparam>
/// <remarks>
/// <para>If the list of default values is not effective as well, null is returned.</para>
/// <para>It is still possible that the result is not effective if both <paramref name="value"/>
/// and all items in <paramref name="deflt"/> are <c>null</c> (or the list itself is <c>null</c>).</para>
/// </remarks>
public static T IfNull <T> (this T value, IEnumerable <T> deflts)
where T : class
{
if (value != null || deflts == null)
{
return(value);
}
else
{
return(Enumerable.FirstOrDefault(deflts, StandardFunctions.NotNull <T> ().Invoke));
}
}
