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

        public void Add(Object key, Object value) {
            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)) {
                    throw new ArgumentException(Environment.GetResourceString("Argument_AddingDuplicate__", node.key, key));
                } 
                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++;
        }