Consistent nil/empty handling

identifier/identifier.go

@@ -122,6 +122,9 @@ func IdentifierAndName(pbIdent *corepb.Identifier, name string) (ACMEIdentifier,
 // Deprecated: TODO(#7311): This can be removed after DnsNames are no longer
 // used in RPCs.
 func IdentifiersAndNames(pbIdents []*corepb.Identifier, names []string) ([]ACMEIdentifier, []string) {
+	if len(pbIdents) == 0 && len(names) == 0 {
+		return nil, nil
+	}
 	if len(pbIdents) == 0 {
 		idents := make([]ACMEIdentifier, len(names))
 		for i, name := range names {

identifier/identifier_test.go

@@ -143,15 +143,15 @@ func TestIdentifiersAndNames(t *testing.T) {
 			Name:         "Empty identifiers, empty names",
 			InputIdents:  []*corepb.Identifier{},
 			InputNames:   []string{},
-			ExpectIdents: []ACMEIdentifier{},
-			ExpectNames:  []string{},
+			ExpectIdents: nil,
+			ExpectNames:  nil,
 		},
 		{
 			Name:         "Empty identifiers, nil names",
 			InputIdents:  []*corepb.Identifier{},
 			InputNames:   nil,
-			ExpectIdents: []ACMEIdentifier{},
-			ExpectNames:  []string{},
+			ExpectIdents: nil,
+			ExpectNames:  nil,
 		},
 		{
 			Name:        "Nil identifiers, populated names",
@@ -167,15 +167,15 @@ func TestIdentifiersAndNames(t *testing.T) {
 			Name:         "Nil identifiers, empty names",
 			InputIdents:  nil,
 			InputNames:   []string{},
-			ExpectIdents: []ACMEIdentifier{},
-			ExpectNames:  []string{},
+			ExpectIdents: nil,
+			ExpectNames:  nil,
 		},
 		{
 			Name:         "Nil identifiers, nil names",
 			InputIdents:  nil,
 			InputNames:   nil,
-			ExpectIdents: []ACMEIdentifier{},
-			ExpectNames:  []string{},
+			ExpectIdents: nil,
+			ExpectNames:  nil,
 		},
 	}