Resolve 'basic_string::_M_construct null not valid' error when no database is provided in connection string

libgnucash/backend/dbi/gnc-backend-dbi.cpp

@@ -159,6 +159,7 @@ UriStrings::UriStrings(const std::string& uri)
                            &password, &dbname);
     m_protocol = std::string{scheme};
     m_host = std::string{host};
+    if (dbname)
 	m_dbname = std::string{dbname};
     if (username)
         m_username = std::string{username};