From 302ac88bdbedb11020ba82a8f715f3cb0bd6290a Mon Sep 17 00:00:00 2001
From: Sven Rebhan <36194019+srebhan@users.noreply.github.com>
Date: Thu, 13 Apr 2023 00:15:35 +0200
Subject: [PATCH] fix(parsers.grok): Fix nil metric for multiline inputs
 (#13078)

---
 plugins/parsers/grok/parser.go      |  4 +++-
 plugins/parsers/grok/parser_test.go | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/plugins/parsers/grok/parser.go b/plugins/parsers/grok/parser.go
index f3c4655ab..d052e1d91 100644
--- a/plugins/parsers/grok/parser.go
+++ b/plugins/parsers/grok/parser.go
@@ -387,7 +387,9 @@ func (p *Parser) Parse(buf []byte) ([]telegraf.Metric, error) {
 		if err != nil {
 			return nil, err
 		}
-		metrics = append(metrics, m)
+		if m != nil {
+			metrics = append(metrics, m)
+		}
 		return metrics, nil
 	}
 
diff --git a/plugins/parsers/grok/parser_test.go b/plugins/parsers/grok/parser_test.go
index 18c2324f1..607751fc0 100644
--- a/plugins/parsers/grok/parser_test.go
+++ b/plugins/parsers/grok/parser_test.go
@@ -1167,3 +1167,19 @@ func TestTrimRegression(t *testing.T) {
 	)
 	require.Equal(t, expected, actual)
 }
+
+func TestMultilineNilMetric(t *testing.T) {
+	buf, err := os.ReadFile("./testdata/test_multiline.log")
+	require.NoError(t, err)
+
+	p := &Parser{
+		Measurement: "multiline",
+		Patterns:    []string{`%{TIMESTAMP_ISO8601:timestamp:ts-rfc3339} Info%{MULTILINEDATA:text}`},
+		Multiline:   true,
+		Log:         testutil.Logger{},
+	}
+	require.NoError(t, p.Compile())
+	actual, err := p.Parse(buf)
+	require.NoError(t, err)
+	require.Empty(t, actual)
+}