From 580876751f2d95a76b9ab1795ffe5847c0d5fed8 Mon Sep 17 00:00:00 2001
From: Emad Mohamadi <emad.mohamadi@booking.com>
Date: Wed, 31 May 2023 13:50:16 +0200
Subject: [PATCH] Fix panic on number of args in fallbackSeries func

---
 pkg/expr/functions/fallbackSeries/function.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pkg/expr/functions/fallbackSeries/function.go b/pkg/expr/functions/fallbackSeries/function.go
index debec7aa..d78535f6 100644
--- a/pkg/expr/functions/fallbackSeries/function.go
+++ b/pkg/expr/functions/fallbackSeries/function.go
@@ -33,6 +33,10 @@ func (f *fallbackSeries) Do(ctx context.Context, e parser.Expr, from, until int3
 		Takes a wildcard seriesList, and a second fallback metric.
 		If the wildcard does not match any series, draws the fallback metric.
 	*/
+	if len(e.Args()) < 2 {
+		return nil, parser.ErrMissingArgument
+	}
+
 	seriesList, err := helper.GetSeriesArg(ctx, e.Args()[0], from, until, values, getTargetData)
 	fallback, errFallback := helper.GetSeriesArg(ctx, e.Args()[1], from, until, values, getTargetData)
 	if errFallback != nil && err != nil {