amp.bus.EnvelopeContext.this C# (CSharp) Метод

        public object this[string key]
        {
            get
            {
                object value = null;

                if (this.Properties.ContainsKey(key))
                {
                    value = this.Properties[key];
                }

                return value;
            }
            set
            {
                this.Properties[key] = value;
            }
        }