Fix httpjson split issue on empty root array (#32001) (#33103)

* Fix httpjson split issue on empty root arrayPublish events

* update asciidoc

* update changelog

* remove old lines

(cherry picked from commit 0334634)

Co-authored-by: Krishna Chaitanya Reddy Burri <krish.reddy91@gmail.com>

CHANGELOG.next.asciidoc

@@ -41,6 +41,8 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 *Filebeat*
 
 - Fix handling of Cisco 302020 messages in ASA and FTD modules. {pull}33089[33089]
+- Fix handling of empty array in httpjson input. {pull}32001[32001]
+
 
 *Heartbeat*
 

x-pack/filebeat/input/httpjson/split.go

@@ -136,6 +136,7 @@ func (s *split) split(ctx *transformContext, root mapstr.M, ch chan<- maybeMsg)
 				return nil
 			}
 			if s.isRoot {
+				ch <- maybeMsg{msg: root}
 				return errEmptyRootField
 			}
 			ch <- maybeMsg{msg: root}

x-pack/filebeat/input/httpjson/split_test.go

@@ -277,10 +277,11 @@ func TestSplit(t *testing.T) {
 			},
 		},
 		{
-			name: "First level split skips publish if no events",
+			name: "First level split publishes with key if no events",
 			config: &splitConfig{
-				Target: "body.response",
-				Type:   "array",
+				Target:     "body.response",
+				Type:       "array",
+				KeepParent: true,
 				Split: &splitConfig{
 					Target:     "body.Event.Attributes",
 					KeepParent: true,
@@ -292,8 +293,12 @@ func TestSplit(t *testing.T) {
 					"response": []interface{}{},
 				},
 			},
-			expectedMessages: []mapstr.M{},
-			expectedErr:      errEmptyRootField,
+			expectedMessages: []mapstr.M{
+				{
+					"response": []interface{}{},
+				},
+			},
+			expectedErr: errEmptyRootField,
 		},
 		{
 			name: "Changes must be local to parent when nested splits",