From 758741f9e2802fee05a3ee77a7c2ab9c6e588826 Mon Sep 17 00:00:00 2001
From: Josh Suereth <joshuasuereth@google.com>
Date: Mon, 4 Oct 2021 09:31:42 -0400
Subject: [PATCH] Fix #314 - Cannot distinguish between sum being 0 and
 undefined.

---
 opentelemetry/proto/metrics/v1/metrics.proto | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/opentelemetry/proto/metrics/v1/metrics.proto b/opentelemetry/proto/metrics/v1/metrics.proto
index 60f5810c0..63bedfe80 100644
--- a/opentelemetry/proto/metrics/v1/metrics.proto
+++ b/opentelemetry/proto/metrics/v1/metrics.proto
@@ -442,7 +442,7 @@ message HistogramDataPoint {
   // Negative events *can* be recorded, but sum should not be filled out when
   // doing so.  This is specifically to enforce compatibility w/ OpenMetrics,
   // see: https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#histogram
-  double sum = 5;
+  optional double sum = 5;
 
   // bucket_counts is an optional field contains the count values of histogram
   // for each bucket.