/// <summary>Returns null if <paramref name="self" /> is <see cref="String.IsNullOrEmpty" />.</summary>
/// <param name="self"></param>
/// <returns></returns>
[CanBeNull]
[DebuggerStepThrough]
[Pure]
public static String? NullIfEmpty( [CanBeNull] this String? self ) => String.IsNullOrEmpty( self ) ? null : self;