fix(alb): allow actions with no TargetGroup

core/alarms/alb-target-group.ts

@@ -55,7 +55,7 @@ export function findLoadBalancersForTargetGroup (targetGroupLogicalId: string, c
   for (const [listenerRuleLogicalId, listenerRule] of Object.entries(listenerRuleResources)) {
     for (const action of listenerRule.Properties?.Actions ?? []) {
       const targetGroupArn = action.TargetGroupArn
-      if (targetGroupArn.Ref === targetGroupLogicalId) {
+      if (typeof targetGroupArn === 'object' && targetGroupArn.Ref === targetGroupLogicalId) {
         allListenerRules[listenerRuleLogicalId] = listenerRule
         break
       }

core/alarms/tests/alb-target-group.test.ts

@@ -79,6 +79,7 @@ test('findLoadBalancersForTargetGroup', (t) => {
     t.equal(loadBalancerLogicalIds.length, 0)
     t.end()
   })
+
   test('finds load balancers through listener rule target groups', (t) => {
     const compiledTemplate = {
       Resources: {
@@ -189,6 +190,29 @@ test('findLoadBalancersForTargetGroup', (t) => {
   t.end()
 })
 
+test('handles actions without a target group', (t) => {
+  const compiledTemplate = {
+    Resources: {
+      listenerRuleA: {
+        Type: 'AWS::ElasticLoadBalancingV2::ListenerRule',
+        Properties: {
+          Actions: [{ AuthenticateOidcConfig: {} }],
+          ListenerArn: { Ref: 'listener' }
+        }
+      },
+      listener: {
+        Type: 'AWS::ElasticLoadBalancingV2::Listener',
+        Properties: {
+          LoadBalancerArn: 'arn:aws:elasticloadbalancing:us-west-2:123456789012:loadbalancer/app/my-load-balancer/50dc6c495c0c9188'
+        }
+      }
+    }
+  }
+  const loadBalancerLogicalIds = findLoadBalancersForTargetGroup('tgA', compiledTemplate)
+  t.equal(loadBalancerLogicalIds.length, 0)
+  t.end()
+})
+
 test('ALB Target Group alarms are created', (t) => {
   const testConfig = createTestConfig(
     defaultConfig.alarms,