[9.0](backport #45361) x-pack/filebeat/input/httpjson: allow empty cursor template values to be ignored by health status updates

CHANGELOG.next.asciidoc

@@ -230,6 +230,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Add Fleet status updating to HTTP JSON input. {issue}44282[44282] {pull}44365[44365]
 - Added input metrics to Azure Blob Storage input. {issue}36641[36641] {pull}43954[43954]
 - Added support for websocket keep_alive heartbeat in the streaming input. {issue}42277[42277] {pull}44204[44204]
+- Allow empty HTTPJSON cursor template value evaluations to be ignored by Fleet health status updates. {pull}45361[45361]
 
 *Auditbeat*
 

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

@@ -53,14 +53,25 @@ func (c *cursor) update(trCtx *transformContext) {
 	}
 
 	for k, cfg := range c.cfg {
-		v, _ := cfg.Value.Execute(trCtx, transformable{}, k, cfg.Default, c.status, c.log)
+		stat := c.status
+		if cfg.mustIgnoreEmptyValue() {
+			stat = ignoreEmptyValueReporter{stat}
+		}
+		v, _ := cfg.Value.Execute(trCtx, transformable{}, k, cfg.Default, stat, c.log)
 		if v != "" || !cfg.mustIgnoreEmptyValue() {
 			_, _ = c.state.Put(k, v)
 			c.log.Debugf("cursor.%s stored with %s", k, v)
 		}
 	}
 }
 
+// ignoreEmptyValueReporter is an abuse of the type system to allow the cursor
+// update mechanism to signal to valueTpl.Execute not to report empty values
+// as health degraded.
+type ignoreEmptyValueReporter struct {
+	status.StatusReporter
+}
+
 func (c *cursor) clone() mapstr.M {
 	if c == nil || c.state == nil {
 		return mapstr.M{}

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

@@ -111,7 +111,9 @@
 			val, err = fallback(errExecutingTemplate)
 		}
 		if err != nil {
-			stat.UpdateStatus(status.Degraded, fmt.Sprintf("failed to execute template %s: %v", targetName, err))
+			if _, ignoreEmpty := stat.(ignoreEmptyValueReporter); !ignoreEmpty || !errors.Is(err, errEmptyTemplateResult) {
+				stat.UpdateStatus(status.Degraded, fmt.Sprintf("failed to execute template %s: %v", targetName, err))
+			}
 			log.Debugw("template execution failed", "target", targetName, "error", err)
 		}
 		tryDebugTemplateValue(targetName, val, log)
@@ -329,7 +331,7 @@
 	case reflect.Float32, reflect.Float64:
 		return int64(vv.Float())
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
 		return int64(vv.Uint())
 	case reflect.String:
 		f, _ := strconv.ParseFloat(vv.String(), 64)
 		return int64(f)