public static void SafeDecrementBy <T>(this IDecrementableCounter <T> counter, T value)
 {
     if (counter != null)
     {
         counter.DecrementBy(value);
     }
 }
 public static void SafeDecrement(this IDecrementableCounter counter)
 {
     if (counter != null)
     {
         counter.Decrement();
     }
 }