code: protected void checkDbSettings() {
          final DatabaseSettings db = settings.getDatabaseSettings();
  
          if(db == null) {
              throw new RuntimeException("You must specify db settings." +
                      " If you don't need a database, simply leave the section blank.");
          }
  
          // CHECKSTYLE:OFF conditional complexity too large
          if(db.getPersistenceUnit() != null &&
            (db.getDriver() != null ||
             db.getDialectClass() != null ||
             db.getJdbcUrl() != null ||
             db.getUser() != null ||
             db.getPass() != null)) {
          // CHECKSTYLE:ON
              throw new IllegalStateException("Cannot set persist-unit with any other database settings");
          }
      }
docs: Runs checks over the database settings before building a {@link CroquetWicket} instance.