segfault if storageClassName not defined

[Julusian]

If I don't define storageClassName, then the provisioner will segfault. While this may be unlikely, I hit this because I have a bunch of pvc resources which I am moving across to this provisioner, and a lot of them specify the class via an annotation (I wrote them years ago)

I0517 22:29:47.841178       1 controller.go:926] provision "ci/builds-minio-data" class "zfs-array": started
I0517 22:29:47.841397       1 controller.go:926] provision "ci/builds-minio-config" class "zfs-array": started
E0517 22:29:47.843664       1 runtime.go:69] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference)
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:76
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:65
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:51
/home/travis/.gimme/versions/go1.10.8.linux.amd64/src/runtime/asm_amd64.s:573
/home/travis/.gimme/versions/go1.10.8.linux.amd64/src/runtime/panic.go:502
/home/travis/.gimme/versions/go1.10.8.linux.amd64/src/runtime/panic.go:63
/home/travis/.gimme/versions/go1.10.8.linux.amd64/src/runtime/signal_unix.go:388
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/provisioner/provisioner.go:243
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:1014
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:786
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:759
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:683
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:697
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:657
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:616
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:133
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:134
/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:88
/home/travis/.gimme/versions/go1.10.8.linux.amd64/src/runtime/asm_amd64.s:2361
I0517 22:29:47.843651       1 event.go:221] Event(v1.ObjectReference{Kind:"PersistentVolumeClaim", Namespace:"ci", Name:"builds-minio-data", UID:"6347a89e-cba8-47fb-9bf6-979f1ba741db", APIVersion:"v1", ResourceVersion:"106896691", FieldPath:""}): type: 'Normal' reason: 'Provisioning' External provisioner is provisioning volume for claim "ci/builds-minio-data"
I0517 22:29:47.843765       1 event.go:221] Event(v1.ObjectReference{Kind:"PersistentVolumeClaim", Namespace:"ci", Name:"builds-minio-config", UID:"0f0366b2-0c04-4f9c-a98e-a66b6fa1e1ef", APIVersion:"v1", ResourceVersion:"106896687", FieldPath:""}): type: 'Normal' reason: 'Provisioning' External provisioner is provisioning volume for claim "ci/builds-minio-config"
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=0x107fec1]

goroutine 106 [running]:
github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/runtime.HandleCrash(0x0, 0x0, 0x0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:58 +0x107
panic(0x11e5de0, 0x1cc7c60)
	/home/travis/.gimme/versions/go1.10.8.linux.amd64/src/runtime/panic.go:502 +0x229
github.com/nmaupu/freenas-provisioner/provisioner.(*freenasProvisioner).Provision(0xc420401f40, 0xc4200ae69a, 0x6, 0xc4203ec210, 0x28, 0x0, 0x0, 0x0, 0xc420010b98, 0xc420729f80, ...)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/provisioner/provisioner.go:243 +0x61
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).provisionClaimOperation(0xc4204d8000, 0xc420010b98, 0x1cda720, 0xc42073e6e0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:1014 +0xcf8
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).syncClaim(0xc4204d8000, 0x134e0c0, 0xc420010b98, 0x134e0c0, 0xc420010b98)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:786 +0xaf
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).syncClaimHandler(0xc4204d8000, 0xc42073e6e0, 0x14, 0x11804c0, 0xc4200a21d0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:759 +0x8d
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).processNextClaimWorkItem.func1(0xc4204d8000, 0x11804c0, 0xc4200a21d0, 0x0, 0x0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:683 +0xe3
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).processNextClaimWorkItem(0xc4204d8000, 0xc4200b4201)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:697 +0x55
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).runClaimWorker(0xc4204d8000)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:657 +0x2b
github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).(github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.runClaimWorker)-fm()
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:616 +0x2a
github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait.JitterUntil.func1(0xc4205b60a0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:133 +0x54
github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc4205b60a0, 0x3b9aca00, 0x0, 0x1, 0x0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:134 +0xbd
github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait.Until(0xc4205b60a0, 0x3b9aca00, 0x0)
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:88 +0x4d
created by github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller.(*ProvisionController).Run.func1
	/home/travis/gopath/src/github.com/nmaupu/freenas-provisioner/vendor/github.com/kubernetes-sigs/sig-storage-lib-external-provisioner/controller/controller.go:616 +0x3e1