From f00e9978b3fd190b7f226d6db6534ad233e9e72e Mon Sep 17 00:00:00 2001
From: Sven Grossmann <svennergr@gmail.com>
Date: Wed, 11 Sep 2024 10:42:06 +0200
Subject: [PATCH 1/2] fix(detected_fields): always return empty array as `null`

---
 pkg/querier/querier.go         | 7 +++++--
 pkg/storage/detected/fields.go | 3 +++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/pkg/querier/querier.go b/pkg/querier/querier.go
index 2046763e6973..997a4bf7731c 100644
--- a/pkg/querier/querier.go
+++ b/pkg/querier/querier.go
@@ -1113,13 +1113,16 @@ func (q *SingleTenantQuerier) DetectedFields(ctx context.Context, req *logproto.
 			level.Warn(q.logger).Log("msg", "failed to marshal hyperloglog sketch", "err", err)
 			continue
 		}
-
+		p := v.parsers
+		if len(p) == 0 {
+			p = nil
+		}
 		fields[fieldCount] = &logproto.DetectedField{
 			Label:       k,
 			Type:        v.fieldType,
 			Cardinality: v.Estimate(),
 			Sketch:      sketch,
-			Parsers:     v.parsers,
+			Parsers:     p,
 		}
 
 		fieldCount++
diff --git a/pkg/storage/detected/fields.go b/pkg/storage/detected/fields.go
index 9d6a699bc1e1..8dd9dd1a1512 100644
--- a/pkg/storage/detected/fields.go
+++ b/pkg/storage/detected/fields.go
@@ -44,6 +44,9 @@ func (f *UnmarshaledDetectedField) Merge(df *logproto.DetectedField) error {
 	f.Parsers = append(f.Parsers, df.Parsers...)
 	slices.Sort(f.Parsers)
 	f.Parsers = slices.Compact(f.Parsers)
+	if len(f.Parsers) == 0 {
+		f.Parsers = nil
+	}
 
 	return f.Sketch.Merge(sketch)
 }

From 89fde6d6a18f09e4a3b9d4a1984c376c8c59702c Mon Sep 17 00:00:00 2001
From: Sven Grossmann <svennergr@gmail.com>
Date: Wed, 11 Sep 2024 14:08:43 +0200
Subject: [PATCH 2/2] fix test

---
 pkg/querier/querier_test.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pkg/querier/querier_test.go b/pkg/querier/querier_test.go
index 6bb83b453906..eb8b8c3a9754 100644
--- a/pkg/querier/querier_test.go
+++ b/pkg/querier/querier_test.go
@@ -1959,8 +1959,8 @@ func TestQuerier_DetectedFields(t *testing.T) {
 		assert.Equal(t, []string{"logfmt"}, durationField.Parsers)
 		assert.Equal(t, []string{"logfmt"}, floatField.Parsers)
 		assert.Equal(t, []string{"logfmt"}, evenField.Parsers)
-		assert.Equal(t, []string{}, constantField.Parsers)
-		assert.Equal(t, []string{}, variableField.Parsers)
+		assert.Equal(t, []string(nil), constantField.Parsers)
+		assert.Equal(t, []string(nil), variableField.Parsers)
 	},
 	)