Handle oversampling cases without panic

Simple check so we don't consolidate (batch/aggFunc) no points

Author: Aergonus

expr/func_summarize.go

@@ -2,6 +2,7 @@ package expr
 
 import (
 	"fmt"
+	"math"
 
 	"github.com/grafana/metrictank/api/models"
 	"github.com/grafana/metrictank/batch"
@@ -93,7 +94,12 @@ func summarizeValues(serie models.Series, aggFunc batch.AggFunc, interval, start
 			}
 		}
 
-		out = append(out, schema.Point{Val: aggFunc(serie.Datapoints[s:i]), Ts: ts})
+		aggPoint := schema.Point{Val: math.NaN(), Ts: ts}
+		if s != i {
+			aggPoint.Val = aggFunc(serie.Datapoints[s:i])
+		}
+
+		out = append(out, aggPoint)
 	}
 
 	return out

expr/func_summarize_test.go

@@ -191,9 +191,8 @@ func TestSummarizeOversampled(t *testing.T) {
 	// Note that graphite does not accept 10 as default seconds, but dur lib defaults to seconds without units!
 	testSummarize("Oversampled Identity", input, outputSum[0], "5", "sum", false, t)
 	testSummarize("Oversampled Identity", input, outputSum[1], "5", "sum", true, t)
-	//testSummarize("Oversampled Identity", input, outputMax[0], "5", "max", false, t)
-	//testSummarize("Oversampled Identity", input, outputMax[1], "5", "max", true, t)
-	_ = outputMax // Max fails because it can't handle 0 terms, sum does not handle the 0 term check
+	testSummarize("Oversampled Identity", input, outputMax[0], "5", "max", false, t)
+	testSummarize("Oversampled Identity", input, outputMax[1], "5", "max", true, t)
 }
 
 func TestSummarizeNyquistSingleIdentity(t *testing.T) {