Fix nil data blob

Signed-off-by: Joanna Lau <118241363+joannalauu@users.noreply.github.com>

Author: joannalauu

common/persistence/sql/sql_domain_audit_store.go

@@ -182,7 +182,7 @@ func (m *sqlDomainAuditStore) GetDomainAuditLogs(
 
 func getDataBlobBytes(blob *persistence.DataBlob) []byte {
 	if blob == nil {
-		return nil
+		return []byte{}
 	}
 	return blob.Data
 }

common/persistence/sql/sql_domain_audit_store_test.go

@@ -105,9 +105,9 @@ func TestCreateDomainAuditLog(t *testing.T) {
 				expectedRow := &sqlplugin.DomainAuditLogRow{
 					DomainID:            serialization.MustParseUUID("d1111111-1111-1111-1111-111111111111"),
 					EventID:             serialization.MustParseUUID("e1111111-1111-1111-1111-111111111111"),
-					StateBefore:         nil,
+					StateBefore:         []byte{},
 					StateBeforeEncoding: "",
-					StateAfter:          nil,
+					StateAfter:          []byte{},
 					StateAfterEncoding:  "",
 					OperationType:       persistence.DomainAuditOperationTypeCreate,
 					CreatedTime:         now,
@@ -441,7 +441,7 @@ func TestGetDataBlobBytes(t *testing.T) {
 	}{
 		"nil blob": {
 			input:    nil,
-			expected: nil,
+			expected: []byte{},
 		},
 		"blob with data": {
 			input: &persistence.DataBlob{