Safe way for get using Dictonary

DictionaryProxy.cs

public class DictionaryProxy<TKey, TValue>: Dictionary<TKey, TValue>
{
    private Dictionary<TKey, TValue> _data;

    public DictionaryProxy(Dictionary<TKey, TValue> data = null)
    {
        _data = data ?? new Dictionary<TKey, TValue>();
    }

    public TValue this[TKey key]
    {
        get
        {
            if (_data != null && _data.ContainsKey(key))
                return _data[key];

            return default(TValue);
        }
        set
        {
            _data[key] = value;
        }
    }
}