code: @OverrideOnDemand
    @Nullable
    protected ICommonsMap <String, String> validateCustomInputParameters (@Nonnull final WPECTYPE aWPEC,
                                                                          @Nullable final DATATYPE aSelectedObject,
                                                                          @Nonnull final FormErrorList aFormErrors,
                                                                          @Nonnull final EWebPageFormAction eFormAction)
    {
      return null;
    }
docs: Validate custom data of the input field.
  
  @param aWPEC
  Current web page execution context. Never <code>null</code>.
  @param aSelectedObject
  The selected object. May be <code>null</code>.
  @param aFormErrors
  The form errors to be filled. Never <code>null</code>.
  @param eFormAction
  The form action mode. Either create, copy or edit.
  @return The custom parameter to be added to the used upon success. If an
  error occurred, this map may be <code>null</code>.