fix(readers): avoid panic on sparse problem responses

internal/commands/readers/readers.go

@@ -257,10 +257,8 @@ func addReader(ctx context.Context, cmd *cli.Command) error {
 	}
 
 	reader, err := appCtx.Client.Readers.Create(ctx, merchantCode, body)
-	if pErr := new(sumup.Problem); errors.As(err, &pErr) {
-		return fmt.Errorf("create reader: %v %v", *pErr.Detail, *pErr.Title)
-	} else if err != nil {
-		return fmt.Errorf("create reader: %w", err)
+	if err != nil {
+		return formatCreateReaderError(err)
 	}
 
 	if appCtx.JSONOutput {
@@ -277,6 +275,13 @@ func addReader(ctx context.Context, cmd *cli.Command) error {
 	})
 }
 
+func formatCreateReaderError(err error) error {
+	if pErr := new(sumup.Problem); errors.As(err, &pErr) {
+		return fmt.Errorf("create reader: %w", pErr)
+	}
+	return fmt.Errorf("create reader: %w", err)
+}
+
 func deleteReader(ctx context.Context, cmd *cli.Command) error {
 	appCtx, err := app.GetAppContext(cmd)
 	if err != nil {

internal/commands/readers/readers_test.go

@@ -1,8 +1,10 @@
 package readers
 
 import (
+	"strings"
 	"testing"
 
+	sumup "github.com/sumup/sumup-go"
 	"github.com/urfave/cli/v3"
 )
 
@@ -18,6 +20,17 @@ func TestContextAwareReaderCommandsDoNotRequireMerchantCodeFlag(t *testing.T) {
 	}
 }
 
+func TestCreateReaderProblemErrorDoesNotPanicOnMissingFields(t *testing.T) {
+	err := formatCreateReaderError(&sumup.Problem{})
+
+	if err == nil {
+		t.Fatal("expected formatted error")
+	}
+	if !strings.Contains(err.Error(), "create reader:") {
+		t.Fatalf("error = %q, want create reader prefix", err.Error())
+	}
+}
+
 func findSubcommand(t *testing.T, cmd *cli.Command, name string) *cli.Command {
 	t.Helper()