Fix jsonpb to emit zero values for Map, Slice, Ptr when EmitDefaults=…

…true

When jsonpb.Marshaler.EmitDefaults is set to true, marshal zero values of the 
following types accordingly:
Map to {}
Slice to []
Ptr to null

jsonpb/jsonpb.go

@@ -207,7 +207,7 @@ func (m *Marshaler) marshalObject(out *errWriter, v proto.Message, indent, typeU
 
 		// IsNil will panic on most value kinds.
 		switch value.Kind() {
-		case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
+		case reflect.Chan, reflect.Func, reflect.Interface:
 			if value.IsNil() {
 				continue
 			}
@@ -235,6 +235,10 @@ func (m *Marshaler) marshalObject(out *errWriter, v proto.Message, indent, typeU
 				if value.Len() == 0 {
 					continue
 				}
+			case reflect.Map, reflect.Ptr, reflect.Slice:
+				if value.IsNil() {
+					continue
+				}
 			}
 		}
 
@@ -402,6 +406,12 @@ func (m *Marshaler) marshalValue(out *errWriter, prop *proto.Properties, v refle
 	var err error
 	v = reflect.Indirect(v)
 
+	// Handle nil pointer
+	if v.Kind() == reflect.Invalid {
+		out.write("null")
+		return out.err
+	}
+
 	// Handle repeated elements.
 	if v.Kind() == reflect.Slice && v.Type().Elem().Kind() != reflect.Uint8 {
 		out.write("[")

jsonpb/jsonpb_test.go

@@ -350,6 +350,9 @@ var marshalingTests = []struct {
 		`{"rFunny":[1,2]}`},
 	{"empty value", marshaler, &pb.Simple3{}, `{}`},
 	{"empty value emitted", Marshaler{EmitDefaults: true}, &pb.Simple3{}, `{"dub":0}`},
+	{"empty repeated emitted", Marshaler{EmitDefaults: true}, &pb.SimpleSlice3{}, `{"slices":[]}`},
+	{"empty map emitted", Marshaler{EmitDefaults: true}, &pb.SimpleMap3{}, `{"stringy":{}}`},
+	{"nested struct null", Marshaler{EmitDefaults: true}, &pb.SimpleNull3{}, `{"simple":null}`},
 	{"map<int64, int32>", marshaler, &pb.Mappy{Nummy: map[int64]int32{1: 2, 3: 4}}, `{"nummy":{"1":2,"3":4}}`},
 	{"map<int64, int32>", marshalerAllOptions, &pb.Mappy{Nummy: map[int64]int32{1: 2, 3: 4}}, nummyPrettyJSON},
 	{"map<string, string>", marshaler,

jsonpb/jsonpb_test_proto/more_test_objects.proto

@@ -37,6 +37,18 @@ message Simple3 {
   double dub = 1;
 }
 
+message SimpleSlice3 {
+  repeated string slices = 1;
+}
+
+message SimpleMap3 {
+  map<string,string> stringy = 1;
+}
+
+message SimpleNull3 {
+  Simple3 simple = 1;
+}
+
 enum Numeral {
   UNKNOWN = 0;
   ARABIC = 1;