[source,csharp]
----
using System;
using System.Text.RegularExpressions;

public static class Program
{
    public static string RemoveVowels(this string value)
    {
        if (value == null)
        {
            return null;
        }
        return Regex.Replace(value, "[aeoui]*","", RegexOptions.IgnoreCase);
    }

    public static void Main()
    {
        Console.WriteLine(((string?)null).RemoveVowels());  // Compliant: 'RemoveVowels' is an extension method
    }
}
----