fix(scheduler): backport nil-scenario preempt guard to v0.15 (#1699)

Signed-off-by: Erez Freiberger <enoodle@gmail.com>

Author: enoodle

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 ### Fixed
 - Fixed default node-scale-adjuster image name (`node-scale-adjuster` → `nodescaleadjuster`) so it matches the image published to GHCR
 - Account for native sidecar containers (initContainers with `restartPolicy: Always`, KEP-753) in pod resource accounting, matching kubelet's `AggregateContainerRequests`. Previously, native sidecar requests were max'd against regular containers instead of summed with them, causing the scheduler to bind pods that kubelet then rejected at admission with `OutOfCpu`/`OutOfGpu`. [#1556](https://github.com/kai-scheduler/KAI-Scheduler/pull/1556)
+- Fixed scheduler nil-pointer panic in the preempt scenario builder when a (partial) job has no tasks to allocate (`NewIdleGpusFilter` dereferenced a nil scenario); added the missing nil-guard matching the sibling filters [#1664](https://github.com/kai-scheduler/KAI-Scheduler/issues/1664) [sam-huang1223](https://github.com/sam-huang1223)
 
 ## [v0.15.2] - 2026-06-10
 
@@ -22,6 +23,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Changed
 - Updated Go toolchain and base build images to v1.26.3.
+- Fixed Helm chart not wiring `podgrouper.queueLabelKey` into `spec.global.queueLabelKey` on the Config CR, so custom queue label keys were ignored at install time [#1655](https://github.com/kai-scheduler/KAI-Scheduler/pull/1655) [dttung2905](https://github.com/dttung2905)
 
 ## [v0.15.0] - 2026-05-20
 

pkg/scheduler/actions/common/solvers/accumulated_scenario_filters/idle_gpus/idle_gpus.go

@@ -53,6 +53,9 @@ type AccumulatedIdleGpus struct {
 
 func NewIdleGpusFilter(
 	scenario *scenario.ByNodeScenario, nodeInfosMap map[string]*node_info.NodeInfo) *AccumulatedIdleGpus {
+	if scenario == nil {
+		return nil
+	}
 	idleGpusMap, relevantNodesSorted := createGpuMap(nodeInfosMap, len(scenario.PendingTasks()))
 
 	filter := &AccumulatedIdleGpus{

pkg/scheduler/actions/common/solvers/accumulated_scenario_filters/idle_gpus/idle_gpus_test.go

@@ -1378,3 +1378,9 @@ func TestAccumulatedIdleGpus_Filter(t *testing.T) {
 		})
 	}
 }
+
+func Test_NewIdleGpusFilter_NilScenario(t *testing.T) {
+	if filter := NewIdleGpusFilter(nil, map[string]*node_info.NodeInfo{}); filter != nil {
+		t.Fatalf("expected nil filter for nil scenario, got %#v", filter)
+	}
+}

pkg/scheduler/actions/common/solvers/pod_scenario_builder.go

@@ -115,6 +115,9 @@ func (asb *PodAccumulatedScenarioBuilder) GetNextScenario() *solverscenario.ByNo
 // outer state. advanceFirst controls whether the first pass starts by popping a
 // victim or by evaluating the current state as-is.
 func (asb *PodAccumulatedScenarioBuilder) iterate(advanceFirst bool) *solverscenario.ByNodeScenario {
+	if asb.lastScenario == nil {
+		return nil
+	}
 	needAdvance := advanceFirst
 	for {
 		if sub := asb.nextFromSubEmitter(); sub != nil {

pkg/scheduler/actions/common/solvers/pod_scenario_builder_test.go

@@ -284,6 +284,24 @@ var _ = Describe("PodAccumulatedScenarioBuilder", func() {
 			Expect(numberOfGeneratedScenarios).To(Equal(len(potentialVictimsPerScenario)))
 		})
 	})
+
+	Context("preemptor with no tasks to allocate - nil scenario", func() {
+		BeforeEach(func() {
+			ssn, _ = initializeSession(0, 0)
+			submitQueue := createQueue("team-a")
+			ssn.ClusterInfo.Queues[submitQueue.UID] = submitQueue
+			// Running tasks are not allocatable, so the job has no tasks to allocate.
+			reclaimerJob, _ = createJobWithTasks(1, 1, "team-a", v1.PodRunning, []v1.ResourceRequirements{})
+			recordedVictimsJobs := []*podgroup_info.PodGroupInfo{}
+			victimsQueue := utils.GetVictimsQueue(ssn, nil)
+
+			scenarioBuilder = NewPodAccumulatedScenarioBuilder(ssn, reclaimerJob, recordedVictimsJobs, victimsQueue, ssn.ClusterInfo.Nodes)
+		})
+		It("does not panic and yields no scenario", func() {
+			Expect(scenarioBuilder.GetValidScenario()).To(BeNil())
+			Expect(scenarioBuilder.GetNextScenario()).To(BeNil())
+		})
+	})
 })
 
 func initializeSession(jobsCount, tasksPerJob int) (*framework.Session, []*pod_info.PodInfo) {