code: public void addFieldError (@Nonnull @Nonempty final String sFieldName, @Nonnull @Nonempty final String sText)
    {
      add (SingleError.builderError ().setErrorFieldName (sFieldName).setErrorText (sText).build ());
    }
docs: Add a field specific error message.
  
  @param sFieldName
  The field name for which the message is to be recorded. May neither
  be <code>null</code> nor empty.
  @param sText
  The text to use. May neither be <code>null</code> nor empty.