Generated protobuf messages require a value

[peschkaj]

Generated protocol buffers messages require a value for enums. This appears to be an artifact of how protogen.exe is generating code plus the fact that enums are value types. For example:

enum RpbReplMode {
    FALSE = 0;
    REALTIME = 1;
    FULLSYNC = 2;
    TRUE = 3;
}
optional RpbReplMode repl = 24;

In this scenario, a property for RpbReplMode is generated that looks like:

private RpbBucketProps.RpbReplMode _repl = RpbBucketProps.RpbReplMode.;
[global::ProtoBuf.ProtoMember(24, IsRequired = false, Name=@"repl", DataFormat = global::ProtoBuf.DataFormat.TwosComplement)]
[global::System.ComponentModel.DefaultValue(RpbBucketProps.RpbReplMode.)]
public RpbBucketProps.RpbReplMode repl
{
  get { return _repl; }
  set { _repl = value; }
}

The code is invalid as generated - there's no default values listed for RpbBucketProps.RpbReplMode, nor should there be since it's optional. Not sure if this is an issue in protogen.exe or in how we're calling it.