code: @Override
      public DataSource getSelectedDataSource() {
          final String dataSourceName = selectableDataSourceHolder.getCurrentSelectableDataSourceKey();
          if (dataSourceName != null) {
              return selectableDataSourceHolder.getSelectedDataSource();
          } else { // means no name set on thread local
              try {
                  selectableDataSourceHolder.switchSelectableDataSourceKey(SlaveDBAccessor.MASTER_DB); // as default
                  return selectableDataSourceHolder.getSelectedDataSource();
              } finally {
                  selectableDataSourceHolder.switchSelectableDataSourceKey(null); // restore
              }
          }
      }
docs: Get the real data-source selected. <br>
  This overrides to return data-source for MasterDB as default.
  @return The instance of real data-source. (NotNull)