Fix panic in ingress class validation

If an ingress had no class annotation, nor IngressClassName  at all, and an IngressClass resource was created for the ingress-nginx there was a panic when the controller tried to check the IngressClassName of the Ingress.

internal/ingress/annotations/class/main.go

@@ -63,5 +63,8 @@ func IsValid(ing *networking.Ingress) bool {
 	}
 
 	// 4. with IngressClass
-	return k8s.IngressClass.Name == *ing.Spec.IngressClassName
+	if ing.Spec.IngressClassName != nil {
+		return k8s.IngressClass.Name == *ing.Spec.IngressClassName
+	}
+	return false
 }

internal/ingress/annotations/class/main_test.go

@@ -22,45 +22,71 @@ import (
 	api "k8s.io/api/core/v1"
 	networking "k8s.io/api/networking/v1beta1"
 	meta_v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/ingress-nginx/internal/k8s"
 )
 
 func TestIsValidClass(t *testing.T) {
 	dc := DefaultClass
 	ic := IngressClass
+	k8sic := k8s.IngressClass
+	v1Ready := k8s.IsIngressV1Ready
 	// restore original values after the tests
 	defer func() {
 		DefaultClass = dc
 		IngressClass = ic
+		k8s.IngressClass = k8sic
+		k8s.IsIngressV1Ready = v1Ready
 	}()
 
 	tests := []struct {
 		ingress    string
 		controller string
 		defClass   string
+		annotation bool
+		k8sClass   *networking.IngressClass
+		v1Ready    bool
 		isValid    bool
 	}{
-		{"", "", "nginx", true},
+		{"", "", "nginx", true, nil, false, true},
-		{"", "nginx", "nginx", true},
+		{"", "nginx", "nginx", true, nil, false, true},
-		{"nginx", "nginx", "nginx", true},
+		{"nginx", "nginx", "nginx", true, nil, false, true},
-		{"custom", "custom", "nginx", true},
+		{"custom", "custom", "nginx", true, nil, false, true},
-		{"", "killer", "nginx", false},
+		{"", "killer", "nginx", true, nil, false, false},
-		{"custom", "nginx", "nginx", false},
+		{"custom", "nginx", "nginx", true, nil, false, false},
+		{"", "custom", "nginx", false,
+			&networking.IngressClass{
+				ObjectMeta: meta_v1.ObjectMeta{
+					Name: "custom",
+				},
+			},
+			false, false},
+		{"", "custom", "nginx", false,
+			&networking.IngressClass{
+				ObjectMeta: meta_v1.ObjectMeta{
+					Name: "custom",
+				},
+			},
+			true, false},
 	}
 
-	ing := &networking.Ingress{
-		ObjectMeta: meta_v1.ObjectMeta{
-			Name:      "foo",
-			Namespace: api.NamespaceDefault,
-		},
-	}
-
-	data := map[string]string{}
-	ing.SetAnnotations(data)
 	for _, test := range tests {
-		ing.Annotations[IngressKey] = test.ingress
+		ing := &networking.Ingress{
+			ObjectMeta: meta_v1.ObjectMeta{
+				Name:      "foo",
+				Namespace: api.NamespaceDefault,
+			},
+		}
+
+		data := map[string]string{}
+		ing.SetAnnotations(data)
+		if test.annotation {
+			ing.Annotations[IngressKey] = test.ingress
+		}
 
 		IngressClass = test.controller
 		DefaultClass = test.defClass
+		k8s.IngressClass = test.k8sClass
+		k8s.IsIngressV1Ready = test.v1Ready
 
 		b := IsValid(ing)
 		if b != test.isValid {