Do not encode undefined fields

[oleksiyk]

There is probably no sense in wiring undefined fields in messages. Actually doing so breaks things up on Riak server:

error:data_error:[{zlib,call,3,[]},
 {zlib,inflate,2,[]},
 {zlib,unzip,1,[]},
 {riak_object,
 decode_vclock,2,
 [{file,
 "src/riak_object.erl"},
 {line,798}]},............

Of course you can avoid sending undefined keys in application but its really easier to fix the problem in protobuf.js

[oleksiyk]

Without this small patch you will have to write things like:

var putObj = {
        bucket: self.bucket,
        key: self.key,
        content: {
            value: data,
            content_type: 'binary/octet-stream'
        }
    }

    if(self.vclock){
        putObj.vclock = self.vclock;
    }

    return self.riak.put(putObj)

instead of

return self.riak.put({
        bucket: self.bucket,
        key: self.key,
        vclock: self.vclock, // vclock might be undefined
        content: {
            value: data,
            content_type: 'binary/octet-stream'
        }
})

[nlf]

good call, thanks