✨ decoder now errors out when encountering an empty runtime.RawExtension

When user tries to decode an object, it should always not be empty. This
error gives people hints when they running into this kind of issues. e.g.
kube-apiserver doesn't include the object in the admission review for
deletion events.

pkg/webhook/admission/decode.go

@@ -17,6 +17,8 @@ limitations under the License.
 package admission
 
 import (
+	"fmt"
+
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/serializer"
@@ -36,11 +38,17 @@ func NewDecoder(scheme *runtime.Scheme) (*Decoder, error) {
 
 // Decode decodes the inlined object in the AdmissionRequest into the passed-in runtime.Object.
 // If you want decode the OldObject in the AdmissionRequest, use DecodeRaw.
+// It errors out if req.Object.Raw is empty i.e. containing 0 raw bytes.
 func (d *Decoder) Decode(req Request, into runtime.Object) error {
+	// we error out if rawObj is an empty object.
+	if len(req.Object.Raw) == 0 {
+		return fmt.Errorf("there is no content to decode")
+	}
 	return d.DecodeRaw(req.Object, into)
 }
 
 // DecodeRaw decodes a RawExtension object into the passed-in runtime.Object.
+// It errors out if rawObj is empty i.e. containing 0 raw bytes.
 func (d *Decoder) DecodeRaw(rawObj runtime.RawExtension, into runtime.Object) error {
 	// NB(directxman12): there's a bug/weird interaction between decoders and
 	// the API server where the API server doesn't send a GVK on the embedded
@@ -49,6 +57,11 @@ func (d *Decoder) DecodeRaw(rawObj runtime.RawExtension, into runtime.Object) er
 	// and call unstructured's special Unmarshal implementation, which calls
 	// back into that same decoder :-/
 	// See kubernetes/kubernetes#74373.
+
+	// we error out if rawObj is an empty object.
+	if len(rawObj.Raw) == 0 {
+		return fmt.Errorf("there is no content to decode")
+	}
 	if unstructuredInto, isUnstructured := into.(*unstructured.Unstructured); isUnstructured {
 		// unmarshal into unstructured's underlying object to avoid calling the decoder
 		if err := json.Unmarshal(rawObj.Raw, &unstructuredInto.Object); err != nil {