code: public PersistentSettings saveProperty(DbSession dbSession, String key, @Nullable String value) {
      savePropertyImpl(dbSession, key, value);
      changeNotifier.onGlobalPropertyChange(key, value);
      return this;
    }
docs: Insert property into database if value is not {@code null}, else delete property from
  database. Session is not committed but {@link org.sonar.api.config.GlobalPropertyChangeHandler}
  are executed.