public static void AppendInValue(this IDictionary<string, object> instance, string key, string separator, object value) { Guard.IsNotNull(instance, "instance"); Guard.IsNotNullOrEmpty(key, "key"); Guard.IsNotNullOrEmpty(separator, "separator"); Guard.IsNotNull(value, "value"); instance[key] = instance.ContainsKey(key) ? instance[key] + separator + value : value.ToString(); }