fix(bitbucketdatacenter): prevent adding new repos with empty branch (#5669)

server/forge/bitbucketdatacenter/bitbucketdatacenter.go

@@ -16,6 +16,7 @@ package bitbucketdatacenter
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -202,6 +203,10 @@ func (c *client) Repo(ctx context.Context, u *model.User, rID model.ForgeRemoteI
 		return nil, fmt.Errorf("unable to fetch default branch: %w", err)
 	}
 
+	if b.DisplayID == "" {
+		return nil, errors.New("default branch setting does not exist")
+	}
+
 	perms := &model.Perm{Pull: true, Push: true}
 	_, _, err = bc.Projects.ListWebhooks(ctx, repo.Project.Key, repo.Slug, &bb.ListOptions{})
 	if err == nil {