Fix panic when reschedule policy for allocation can't be looked up

because its task group changed

nomad/structs/structs.go

@@ -6293,6 +6293,10 @@ func (a *Allocation) NextRescheduleTime() (time.Time, bool) {
 // It is calculated according to the delay function and previous reschedule attempts.
 func (a *Allocation) NextDelay() time.Duration {
 	policy := a.ReschedulePolicy()
+	// Can be nil if the task group was updated to remove its reschedule policy
+	if policy == nil {
+		return 0
+	}
 	delayDur := policy.Delay
 	if a.RescheduleTracker == nil || a.RescheduleTracker.Events == nil || len(a.RescheduleTracker.Events) == 0 {
 		return delayDur

nomad/structs/structs_test.go

@@ -2941,6 +2941,12 @@ func TestAllocation_NextDelay(t *testing.T) {
 			expectedRescheduleTime:     time.Time{},
 			expectedRescheduleEligible: false,
 		},
+		{
+			desc:                       "Allocation has no reschedule policy",
+			alloc:                      &Allocation{},
+			expectedRescheduleTime:     time.Time{},
+			expectedRescheduleEligible: false,
+		},
 		{
 			desc: "Allocation lacks task state",
 			reschedulePolicy: &ReschedulePolicy{
@@ -3385,7 +3391,9 @@ func TestAllocation_NextDelay(t *testing.T) {
 		t.Run(tc.desc, func(t *testing.T) {
 			require := require.New(t)
 			j := testJob()
-			j.TaskGroups[0].ReschedulePolicy = tc.reschedulePolicy
+			if tc.reschedulePolicy != nil {
+				j.TaskGroups[0].ReschedulePolicy = tc.reschedulePolicy
+			}
 			tc.alloc.Job = j
 			tc.alloc.TaskGroup = j.TaskGroups[0].Name
 			reschedTime, allowed := tc.alloc.NextRescheduleTime()