app/vmselect/promql: remove zero timeseries from prometheus_buckets output

app/vmselect/promql/transform.go

@@ -343,12 +343,24 @@ func vmrangeBucketsToLE(tss []*timeseries) []*timeseries {
 		ts.MetricName.AddTag("le", leStr)
 		return &ts
 	}
+	isZeroTS := func(ts *timeseries) bool {
+		for _, v := range ts.Values {
+			if v > 0 {
+				return false
+			}
+		}
+		return true
+	}
 	for _, xss := range m {
 		sort.Slice(xss, func(i, j int) bool { return xss[i].end < xss[j].end })
 		xssNew := make([]x, 0, len(xss)+2)
 		var xsPrev x
 		for _, xs := range xss {
 			ts := xs.ts
+			if isZeroTS(ts) {
+				// Skip time series with zeros. They are substituted by xssNew below.
+				continue
+			}
 			if xs.start != xsPrev.end {
 				xssNew = append(xssNew, x{
 					endStr: xs.startStr,