omitempty

staging/src/k8s.io/apiserver/pkg/util/flag/colon_separated_multimap_string_string.go

@@ -48,12 +48,6 @@ func (m *ColonSeparatedMultimapStringString) Set(value string) error {
 	if m.Multimap == nil {
 		return fmt.Errorf("no target (nil pointer to map[string][]string)")
 	}
-	// allow explicit nil multimap
-	if value == "nil" {
-		*m.Multimap = nil
-		m.initialized = true
-		return nil
-	}
 	if !m.initialized || *m.Multimap == nil {
 		// clear default values, or allocate if no existing map
 		*m.Multimap = make(map[string][]string)
@@ -76,10 +70,6 @@ func (m *ColonSeparatedMultimapStringString) Set(value string) error {
 
 // String implements github.com/spf13/pflag.Value
 func (m *ColonSeparatedMultimapStringString) String() string {
-	if *m.Multimap == nil {
-		return "nil"
-	}
-
 	type kv struct {
 		k string
 		v string
@@ -105,3 +95,8 @@ func (m *ColonSeparatedMultimapStringString) String() string {
 func (m *ColonSeparatedMultimapStringString) Type() string {
 	return "colonSeparatedMultimapStringString"
 }
+
+// Empty implements OmitEmpty
+func (m *ColonSeparatedMultimapStringString) Empty() bool {
+	return len(*m.Multimap) == 0
+}

staging/src/k8s.io/apiserver/pkg/util/flag/colon_separated_multimap_string_string_test.go

@@ -28,7 +28,7 @@ func TestStringColonSeparatedMultimapStringString(t *testing.T) {
 		m      *ColonSeparatedMultimapStringString
 		expect string
 	}{
-		{"nil", NewColonSeparatedMultimapStringString(&nilMap), "nil"},
+		{"nil", NewColonSeparatedMultimapStringString(&nilMap), ""},
 		{"empty", NewColonSeparatedMultimapStringString(&map[string][]string{}), ""},
 		{"empty key", NewColonSeparatedMultimapStringString(
 			&map[string][]string{
@@ -85,12 +85,6 @@ func TestSetColonSeparatedMultimapStringString(t *testing.T) {
 			&ColonSeparatedMultimapStringString{
 				initialized: true,
 				Multimap:    &map[string][]string{}}, ""},
-		{"explicitly nil", []string{"nil"},
-			NewColonSeparatedMultimapStringString(&map[string][]string{"default": {}}),
-			&ColonSeparatedMultimapStringString{
-				initialized: true,
-				Multimap:    &nilMap,
-			}, ""},
 		// make sure we still allocate for "initialized" multimaps where Multimap was initially set to a nil map
 		{"allocates map if currently nil", []string{""},
 			&ColonSeparatedMultimapStringString{initialized: true, Multimap: &nilMap},
@@ -225,3 +219,24 @@ func TestRoundTripColonSeparatedMultimapStringString(t *testing.T) {
 		})
 	}
 }
+
+func TestEmptyColonSeparatedMultimapStringString(t *testing.T) {
+	var nilMap map[string][]string
+	cases := []struct {
+		desc   string
+		val    *ColonSeparatedMultimapStringString
+		expect bool
+	}{
+		{"nil", NewColonSeparatedMultimapStringString(&nilMap), true},
+		{"empty", NewColonSeparatedMultimapStringString(&map[string][]string{}), true},
+		{"populated", NewColonSeparatedMultimapStringString(&map[string][]string{"foo": {}}), false},
+	}
+	for _, c := range cases {
+		t.Run(c.desc, func(t *testing.T) {
+			result := c.val.Empty()
+			if result != c.expect {
+				t.Fatalf("expect %t but got %t", c.expect, result)
+			}
+		})
+	}
+}