fix: proto3 optional scalars should default to null in reflection API (#1693)

#1584 made proto3 optional
scalars default to null when using static/static-module, but the old
behaviour remained when using reflection (eg json-module).

Author: dae

src/field.js

@@ -270,6 +270,9 @@ Field.prototype.resolve = function resolve() {
             this.typeDefault = null;
         else // instanceof Enum
             this.typeDefault = this.resolvedType.values[Object.keys(this.resolvedType.values)[0]]; // first defined
+    } else if (this.options && this.options.proto3_optional) {
+        // proto3 scalar value marked optional; should default to null
+        this.typeDefault = null;
     }
 
     // use explicitly set default value if present

tests/comp_optional.js

@@ -22,5 +22,9 @@ tape.test("proto3 optional", function(test) {
     test.equal(Message.oneofs._optionalInt32.name, '_optionalInt32');
     test.deepEqual(Message.oneofs._optionalInt32.oneof, ['optionalInt32']);
 
+    var m = Message.create({});
+    test.strictEqual(m.regularInt32, 0);
+    test.strictEqual(m.optionalInt32, null);
+
     test.end();
 });