Fix scheduled action panic with null event payload (#37459)

This fixes the scheduled action panic when an event payload is JSON
`null` by initializing the payload map before adding `schedule`. It also
adds regression coverage for the null-payload case.

Fixes #37447.

Testing:
- `go test -tags 'sqlite sqlite_unlock_notify' ./services/actions -run
'^TestWithScheduleInEventPayload$' -count=1`
- Local note: this agent ran the command as root with a temporary
`GITEA_TEST_CONF=custom/conf/app-test-root.ini` file that only set
`I_AM_BEING_UNSAFE_RUNNING_AS_ROOT = true`.

Authorship: cyphercodes; AI assistance disclosed: Hermes Agent
(GPT-5.5).

---------

Co-authored-by: cyphercodes <cyphercodes@users.noreply.github.com>
Co-authored-by: Hermes Agent (GPT-5.5) <hermes-agent@users.noreply.github.com>
Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: Giteabot <teabot@gitea.io>

services/actions/schedule_tasks.go

@@ -132,14 +132,22 @@ func CreateScheduleTask(ctx context.Context, spec *actions_model.ActionScheduleS
 }
 
 func withScheduleInEventPayload(eventPayload, schedule string) string {
-	if schedule == "" || eventPayload == "" {
+	if schedule == "" {
 		return eventPayload
 	}
 
-	event := map[string]any{}
-	if err := json.Unmarshal([]byte(eventPayload), &event); err != nil {
-		log.Error("withScheduleInEventPayload: unmarshal: %v", err)
-		return eventPayload
+	// eventPayload originates from json.Marshal(input.Payload) in handleSchedules,
+	// so a nil payload is stored as the literal "null" and pre-existing rows may be
+	// empty. Both cases start from a fresh map so the schedule field can still be set.
+	var event map[string]any
+	if eventPayload != "" {
+		if err := json.Unmarshal([]byte(eventPayload), &event); err != nil {
+			log.Error("withScheduleInEventPayload: unmarshal: %v", err)
+			return eventPayload
+		}
+	}
+	if event == nil {
+		event = map[string]any{}
 	}
 
 	event["schedule"] = schedule

services/actions/schedule_tasks_test.go

@@ -22,9 +22,20 @@ func TestWithScheduleInEventPayload(t *testing.T) {
 		assert.Equal(t, "refs/heads/main", event["ref"])
 	})
 
-	t.Run("keeps empty payload", func(t *testing.T) {
+	t.Run("adds schedule to null payload", func(t *testing.T) {
+		updated := withScheduleInEventPayload("null", "37 12 5 1 2")
+
+		event := map[string]any{}
+		assert.NoError(t, json.Unmarshal([]byte(updated), &event))
+		assert.Equal(t, "37 12 5 1 2", event["schedule"])
+	})
+
+	t.Run("adds schedule to empty payload", func(t *testing.T) {
 		updated := withScheduleInEventPayload("", "37 12 5 1 2")
-		assert.Empty(t, updated)
+
+		event := map[string]any{}
+		assert.NoError(t, json.Unmarshal([]byte(updated), &event))
+		assert.Equal(t, "37 12 5 1 2", event["schedule"])
 	})
 
 	t.Run("keeps payload when schedule empty", func(t *testing.T) {