Added convenience methods for to/from xml and json
diff --git a/src/ProtocolBuffers/GeneratedBuilder.cs b/src/ProtocolBuffers/GeneratedBuilder.cs
index 4d4be21..94948e4 100644
--- a/src/ProtocolBuffers/GeneratedBuilder.cs
+++ b/src/ProtocolBuffers/GeneratedBuilder.cs
@@ -49,7 +49,7 @@
/// </summary>
public abstract class GeneratedBuilder<TMessage, TBuilder> : AbstractBuilder<TMessage, TBuilder>
where TMessage : GeneratedMessage<TMessage, TBuilder>
- where TBuilder : GeneratedBuilder<TMessage, TBuilder>
+ where TBuilder : GeneratedBuilder<TMessage, TBuilder>, new()
{
/// <summary>
/// Returns the message being built at the moment.