serialization of dictionary c# unity

 [Serializable] public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, ISerializationCallbackReceiver {     [SerializeField]     private List<TKey> keys = new List<TKey>();          [SerializeField]     private List<TValue> values = new List<TValue>();          // save the dictionary to lists     public void OnBeforeSerialize()     {         keys.Clear();         values.Clear();         foreach(KeyValuePair<TKey, TValue> pair in this)         {             keys.Add(pair.Key);             values.Add(pair.Value);         }     }          // load dictionary from lists     public void OnAfterDeserialize()     {         this.Clear();          if(keys.Count != values.Count)             throw new System.Exception(string.Format("there are {0} keys and {1} values after deserialization. Make sure that both key and value types are serializable."));          for(int i = 0; i < keys.Count; i++)             this.Add(keys[i], values[i]);     } }