fixes

Signed-off-by: Won Jun Jang <wjang@uber.com>

model/converter/json/from_domain.go

@@ -99,20 +99,19 @@ func (fd fromDomain) convertReferences(span *model.Span, preserveParentID bool)
 	out := make([]json.Reference, 0, length)
 	var parentRefAdded bool
 	for _, ref := range span.References {
-		newRef := json.Reference{
+		out = append(out, json.Reference{
 			RefType: fd.convertRefType(ref.RefType),
 			TraceID: json.TraceID(ref.TraceID.String()),
 			SpanID:  json.SpanID(ref.SpanID.String()),
-		}
-		out = append(out, newRef)
-		if newRef.TraceID == json.TraceID(span.TraceID.String()) &&
-			newRef.SpanID == json.SpanID(span.ParentSpanID.String()) {
+		})
+		if ref.TraceID == span.TraceID && ref.SpanID == span.ParentSpanID {
 			// Check if the parent reference already exists
 			parentRefAdded = true
 		}
 	}
 	if span.ParentSpanID != 0 && !preserveParentID && !parentRefAdded {
-		// TODO this (wrongly) assumes that the reference type is always ChildOf
+		// By this point, if ParentSpanID != 0 but there are no other references,
+		// then the ParentSpanID does refer to child-of type
 		out = append(out, json.Reference{
 			RefType: json.ChildOf,
 			TraceID: json.TraceID(span.TraceID.String()),