public void Ay()
 {
     Assert.AreEqual("ay", StringEx.Ay("left", "y"));
     Assert.AreEqual("", StringEx.Ay("", "y"));
 }
 public static string Join <T>([NotNull, InstantHandle] this IEnumerable <T> values) =>
 // ReSharper disable once BuiltInTypeReferenceStyle
 StringClass.Join("", values);
 // ReSharper disable once BuiltInTypeReferenceStyle
 public static bool NotNullNorWhiteSpace([CanBeNull] this string str) => !StringClass.IsNullOrWhiteSpace(str);
 public static string Join <T>([NotNull, InstantHandle] this IEnumerable <T> values, [CanBeNull] string separator) =>
 // ReSharper disable once BuiltInTypeReferenceStyle
 StringClass.Join(separator, values);