/// <summary>
/// Returns value of the Nested Content property from the source.
/// If property (Nested conten returns null if nothing is created) is null, returns empty enumeration.
/// </summary>
/// <typeparam name="TNestedContent">Type of the NestedContent model.</typeparam>
/// <param name="source">The source.</param>
/// <param name="propertyName">Name of the property.</param>
/// <returns>Value of the NestedContent property. </returns>
public static IEnumerable <TNestedContent> GetNestedContentPropertyValue <TNestedContent>(
this IPublishedElement source, [CallerMemberName] string propertyName = null)
where TNestedContent : INestedContent
=> source.GetPropertyValue <IEnumerable <IPublishedElement> >(propertyName.ToFirstLower()).EmptyIfNull().OfType <TNestedContent>();