code: @Nullable
    @OverrideOnDemand
    protected EBootstrapFormGroupState getFormGroupStateFromErrorList (@Nullable final IErrorList aErrorList)
    {
      if (aErrorList != null && !aErrorList.isEmpty ())
      {
        if (aErrorList.containsAtLeastOneError ())
          return EBootstrapFormGroupState.ERROR;
        if (aErrorList.containsAtLeastOneFailure ())
          return EBootstrapFormGroupState.WARNING;
      }
      return null;
    }
docs: Retrieve an optional CSS class that is provided to the final node. This
  method is only called if a non-<code>null</code> and non-empty error list
  is present.
  
  @param aErrorList
  The error list. May be <code>null</code>.
  @return May be <code>null</code> to indicate no CSS class.