Fix mimir.rules.kubernetes panic on non-leader debug info retrieval (#3451)

* Fix mimir.rules.kubernetes to only return eventProcessor state if it exists

* update CHANGELOG

Author: TheoBrigitte

CHANGELOG.md

@@ -43,6 +43,7 @@ Main (unreleased)
 ### Bugfixes
 
 - Fix `otelcol.receiver.filelog` documentation's default value for `start_at`. (@petewall)
+- Fix `mimir.rules.kubernetes` panic on non-leader debug info retrieval (@TheoBrigitte)
 
 ### Other changes
 

internal/component/mimir/rules/kubernetes/debug.go

@@ -23,6 +23,10 @@ type DebugMimirNamespace struct {
 func (c *Component) DebugInfo() interface{} {
 	var output DebugInfo
 
+	if c.eventProcessor == nil {
+		return output
+	}
+
 	currentState := c.eventProcessor.getMimirState()
 	for namespace := range currentState {
 		if !isManagedMimirNamespace(c.args.MimirNameSpacePrefix, namespace) {