Allow passing null

[lautarodragan]

protobuf.js version: <7.2.0>

Related issue: #677

Hey there! I'm in need of being able to pass null for fields from my public API to private gRPC services.

I understand the best approach for this is using the well-known wrapper types, such as StringValue.

I also want to do automatic wrapping and unwrapping of these wrapper types.

I am able to encode {} for these fields, which I can interpret as absence of value (but presence of key), but I'd like to use null everywhere.

I looked into a few already-existing reported issues, and understand I can override the toObject and fromObject of protobuf.wrappers['.google.protobuf.StringValue'] to achieve this, but this only seems to work in the toObject phase — the fromObject never receives null values.

Example code (js, proto and stdout): https://gist.github.com/lautarodragan/52fd05a9e261b7e22c27f4eae41baf1a

I see the generated code for MyHappyProto.fromObject is this:

(function anonymous(types,util
) {
return function MyHappyProto$fromObject(d){
  if(d instanceof this.ctor)
  return d
  var m=new this.ctor
  if(d.id!=null){
  m.id=String(d.id)
  }
  if(d.name!=null){
  if(typeof d.name!=="object")
  throw TypeError(".MyHappyProto.name: object expected")
  m.name=types[1].fromObject(d.name)
  }
  if(d.address!=null){
  if(typeof d.address!=="object")
  throw TypeError(".MyHappyProto.address: object expected")
  m.address=types[2].fromObject(d.address)
  }
  if(d.something!=null){
  if(typeof d.something!=="object")
  throw TypeError(".MyHappyProto.something: object expected")
  m.something=types[3].fromObject(d.something)
  }
  if(d.nullable!=null){
  if(typeof d.nullable!=="object")
  throw TypeError(".MyHappyProto.nullable: object expected")
  m.nullable=types[4].fromObject(d.nullable)
  }
  return m
}
})

If the field is null, fromObject is not called at all — I get no chance to transform null into {} in the fromObject phase.

I guess these checks come from

protobuf.js/src/converter.js

Lines 144 to 147 in 0099ddc

	("if(d%s!=null){", prop); // !== undefined && !== null
	genValuePartial_fromObject(gen, field, /* not sorted */ i, prop);
	if (!(field.resolvedType instanceof Enum)) gen
	("}");

, but I have no idea because I don't really understand this code gen.

The toObject correctly transforms {} into null and { value: 'string' } into string.

Can these checks be disabled somehow? Otherwise, is there an alternative to fromObject that I can work with?