System.Collections.ListDictionaryInternal.this C# (CSharp) Method

        public Object this[Object key] {
            get {
                if (key == null) {
                    throw new ArgumentNullException("key", Environment.GetResourceString("ArgumentNull_Key"));
                }
                DictionaryNode node = head;

                while (node != null) {
                    if ( node.key.Equals(key) ) {
                        return node.value;
                    }
                    node = node.next;
                }
                return null;
            }
            set {
                if (key == null) {
                    throw new ArgumentNullException("key", Environment.GetResourceString("ArgumentNull_Key"));
                }

                if (!key.GetType().IsSerializable)                 
                    throw new ArgumentException(Environment.GetResourceString("Argument_NotSerializable"), "key");                    

                if( (value != null) && (!value.GetType().IsSerializable ) )
                    throw new ArgumentException(Environment.GetResourceString("Argument_NotSerializable"), "value");                    
                
                version++;
                DictionaryNode last = null;
                DictionaryNode node;
                for (node = head; node != null; node = node.next) {
                    if( node.key.Equals(key) ) {
                        break;
                    } 
                    last = node;
                }
                if (node != null) {
                    // Found it
                    node.value = value;
                    return;
                }
                // Not found, so add a new one
                DictionaryNode newNode = new DictionaryNode();
                newNode.key = key;
                newNode.value = value;
                if (last != null) {
                    last.next = newNode;
                }
                else {
                    head = newNode;
                }
                count++;
            }
        }