panic happened when add podgroup watch

[Crazybean-lwb]

kubeadm version: v1.20.11
k8s version: 1.20.11
I have build training-operator image with this merged pr.
pytorch job can use gang-scheduler, now. However nil pointer problem happened, when training controller build or watch pytorch jobs .
I have detected problem happened, when log event object in https://github.com/kubeflow/training-operator/blob/master/pkg/common/util/reconciler.go#L113
Some exception may happened.

---

errors as follows:

time="2022-10-31T11:55:15Z" level=info msg="PyTorchJob=ddp-vol, ReplicaType=Worker expected=1, running=1, succeeded=0, failed=0, Replicas=1"
E1031 11:56:00.164678       1 runtime.go:79] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference)
goroutine 796 [running]:
k8s.io/apimachinery/pkg/util/runtime.logPanic({0x185a700?, 0x2a0c1a0})
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/runtime/runtime.go:75 +0x99
k8s.io/apimachinery/pkg/util/runtime.HandleCrash({0x0, 0x0, 0xc000064150?})
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/runtime/runtime.go:49 +0x75
panic({0x185a700, 0x2a0c1a0})
	/usr/local/go/src/runtime/panic.go:884 +0x212
github.com/sirupsen/logrus.(*Entry).Logf(0xc0003dca00?, 0x1213940?, {0x1ade9f4?, 0xc000f92050?}, {0xc000d29b48?, 0xc00003c000?, 0x47?})
	/go/pkg/mod/github.com/sirupsen/logrus@v1.8.1/entry.go:337 +0x22
github.com/sirupsen/logrus.(*Entry).Debugf(...)
	/go/pkg/mod/github.com/sirupsen/logrus@v1.8.1/entry.go:347
github.com/kubeflow/training-operator/pkg/common/util.OnDependentUpdateFunc.func1({{0x1d5b0d0?, 0xc00045e000?}, {0x1d5b0d0?, 0xc000624d80?}})
	/workspace/pkg/common/util/reconciler.go:113 +0x4fd
sigs.k8s.io/controller-runtime/pkg/predicate.Funcs.Update(...)
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.12.1/pkg/predicate/predicate.go:88
sigs.k8s.io/controller-runtime/pkg/source/internal.EventHandler.OnUpdate({{0x1d445a0, 0xc0002c5c20}, {0x1d4d7c8, 0xc00099c1a0}, {0xc0008a0d70, 0x1, 0x1}}, {0x1a6fb40?, 0xc00045e000}, {0x1a6fb40, ...})
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.12.1/pkg/source/internal/eventsource.go:88 +0x43d
k8s.io/client-go/tools/cache.(*processorListener).run.func1()
	/go/pkg/mod/k8s.io/client-go@v0.24.1/tools/cache/shared_informer.go:816 +0xf7
k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1(0xc00046ea20?)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:155 +0x3e
k8s.io/apimachinery/pkg/util/wait.BackoffUntil(0xc0007bf738?, {0x1d2b040, 0xc000722c00}, 0x1, 0xc00091a540)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:156 +0xb6
k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc00046ed50?, 0x3b9aca00, 0x0, 0x90?, 0xc0005a0420?)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:133 +0x89
k8s.io/apimachinery/pkg/util/wait.Until(...)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:90
k8s.io/client-go/tools/cache.(*processorListener).run(0xc00036c280?)
	/go/pkg/mod/k8s.io/client-go@v0.24.1/tools/cache/shared_informer.go:812 +0x6b
k8s.io/apimachinery/pkg/util/wait.(*Group).Start.func1()
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:73 +0x5a
created by k8s.io/apimachinery/pkg/util/wait.(*Group).Start
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:71 +0x85
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x14eb0c2]

goroutine 796 [running]:
k8s.io/apimachinery/pkg/util/runtime.HandleCrash({0x0, 0x0, 0xc000064150?})
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/runtime/runtime.go:56 +0xd7
panic({0x185a700, 0x2a0c1a0})
	/usr/local/go/src/runtime/panic.go:884 +0x212
github.com/sirupsen/logrus.(*Entry).Logf(0xc0003dca00?, 0x1213940?, {0x1ade9f4?, 0xc000f92050?}, {0xc000d29b48?, 0xc00003c000?, 0x47?})
	/go/pkg/mod/github.com/sirupsen/logrus@v1.8.1/entry.go:337 +0x22
github.com/sirupsen/logrus.(*Entry).Debugf(...)
	/go/pkg/mod/github.com/sirupsen/logrus@v1.8.1/entry.go:347
github.com/kubeflow/training-operator/pkg/common/util.OnDependentUpdateFunc.func1({{0x1d5b0d0?, 0xc00045e000?}, {0x1d5b0d0?, 0xc000624d80?}})
	/workspace/pkg/common/util/reconciler.go:113 +0x4fd
sigs.k8s.io/controller-runtime/pkg/predicate.Funcs.Update(...)
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.12.1/pkg/predicate/predicate.go:88
sigs.k8s.io/controller-runtime/pkg/source/internal.EventHandler.OnUpdate({{0x1d445a0, 0xc0002c5c20}, {0x1d4d7c8, 0xc00099c1a0}, {0xc0008a0d70, 0x1, 0x1}}, {0x1a6fb40?, 0xc00045e000}, {0x1a6fb40, ...})
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.12.1/pkg/source/internal/eventsource.go:88 +0x43d
k8s.io/client-go/tools/cache.(*processorListener).run.func1()
	/go/pkg/mod/k8s.io/client-go@v0.24.1/tools/cache/shared_informer.go:816 +0xf7
k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1(0xc00046ea20?)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:155 +0x3e
k8s.io/apimachinery/pkg/util/wait.BackoffUntil(0xc0007bf738?, {0x1d2b040, 0xc000722c00}, 0x1, 0xc00091a540)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:156 +0xb6
k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc00046ed50?, 0x3b9aca00, 0x0, 0x90?, 0xc0005a0420?)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:133 +0x89
k8s.io/apimachinery/pkg/util/wait.Until(...)
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:90
k8s.io/client-go/tools/cache.(*processorListener).run(0xc00036c280?)
	/go/pkg/mod/k8s.io/client-go@v0.24.1/tools/cache/shared_informer.go:812 +0x6b
k8s.io/apimachinery/pkg/util/wait.(*Group).Start.func1()
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:73 +0x5a
created by k8s.io/apimachinery/pkg/util/wait.(*Group).Start
	/go/pkg/mod/k8s.io/apimachinery@v0.24.1/pkg/util/wait/wait.go:71 +0x85

Originally posted by @liuweibin6566396837 in #1666 (comment)