code: @Nullable
    @OverrideOnDemand
    protected ICommonsSet <String> onShowSelectedObjectCustomAttrs (@Nonnull final WPECTYPE aWPEC,
                                                                    @Nonnull final DATATYPE aSelectedObject,
                                                                    @Nonnull final Map <String, String> aCustomAttrs,
                                                                    @Nonnull final BootstrapViewForm aViewForm)
    {
      return null;
    }
docs: Callback for manually extracting custom attributes. This method is called
  independently if custom attributes are present or not.
  
  @param aWPEC
  The current web page execution context. Never <code>null</code>.
  @param aSelectedObject
  The object currently shown. Never <code>null</code>.
  @param aCustomAttrs
  The available custom attributes. Never <code>null</code> but maybe
  empty.
  @param aViewForm
  The table to be add custom information
  @return A set of all attribute names that were handled in this method or
  <code>null</code>. All attributes handled in this method will not
  be displayed generically.