fix: handle nil ResourceList in max() to prevent panic

staging/src/k8s.io/kubectl/pkg/util/resource/resource.go

@@ -152,7 +152,12 @@ func determineContainerReqs(pod *corev1.Pod, container *corev1.Container, cs *co
 // max returns the result of max(a, b...) for each named resource and is only used if we can't
 // accumulate into an existing resource list
 func max(a corev1.ResourceList, b ...corev1.ResourceList) corev1.ResourceList {
-	result := a.DeepCopy()
+	var result corev1.ResourceList
+	if a != nil {
+		result = a.DeepCopy()
+	} else {
+		result = corev1.ResourceList{}
+	}
 	for _, other := range b {
 		maxResourceList(result, other)
 	}

staging/src/k8s.io/kubectl/pkg/util/resource/resource_test.go

@@ -0,0 +1,96 @@
+/*
+Copyright The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package resource
+
+import (
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/api/resource"
+)
+
+func TestMaxWithNilResourceList(t *testing.T) {
+	tests := []struct {
+		name string
+		a    corev1.ResourceList
+		b    []corev1.ResourceList
+		want corev1.ResourceList
+	}{
+		{
+			name: "nil first argument with non-nil second",
+			a:    nil,
+			b:    []corev1.ResourceList{{corev1.ResourceCPU: resource.MustParse("100m")}},
+			want: corev1.ResourceList{corev1.ResourceCPU: resource.MustParse("100m")},
+		},
+		{
+			name: "nil first argument with nil second",
+			a:    nil,
+			b:    []corev1.ResourceList{nil},
+			want: corev1.ResourceList{},
+		},
+		{
+			name: "nil first argument with empty second",
+			a:    nil,
+			b:    []corev1.ResourceList{{}},
+			want: corev1.ResourceList{},
+		},
+		{
+			name: "nil first argument with no second arguments",
+			a:    nil,
+			b:    nil,
+			want: corev1.ResourceList{},
+		},
+		{
+			name: "empty first argument with non-nil second",
+			a:    corev1.ResourceList{},
+			b:    []corev1.ResourceList{{corev1.ResourceCPU: resource.MustParse("100m")}},
+			want: corev1.ResourceList{corev1.ResourceCPU: resource.MustParse("100m")},
+		},
+		{
+			name: "non-nil first argument takes max",
+			a:    corev1.ResourceList{corev1.ResourceCPU: resource.MustParse("200m")},
+			b:    []corev1.ResourceList{{corev1.ResourceCPU: resource.MustParse("100m")}},
+			want: corev1.ResourceList{corev1.ResourceCPU: resource.MustParse("200m")},
+		},
+		{
+			name: "second argument larger takes max",
+			a:    corev1.ResourceList{corev1.ResourceCPU: resource.MustParse("100m")},
+			b:    []corev1.ResourceList{{corev1.ResourceCPU: resource.MustParse("200m")}},
+			want: corev1.ResourceList{corev1.ResourceCPU: resource.MustParse("200m")},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := max(tt.a, tt.b...)
+			if len(got) != len(tt.want) {
+				t.Errorf("case %q, expected %d resources but got %d", tt.name, len(tt.want), len(got))
+				return
+			}
+			for name, wantQty := range tt.want {
+				gotQty, ok := got[name]
+				if !ok {
+					t.Errorf("case %q, expected resource %s but it was missing", tt.name, name)
+					continue
+				}
+				if gotQty.Cmp(wantQty) != 0 {
+					t.Errorf("case %q, expected resource %s to be %s but got %s", tt.name, name, wantQty.String(), gotQty.String())
+				}
+			}
+		})
+	}
+}