code: private String getReadonlyDisplayValue(final Object value, final UIInput component, final Converter converter) {
          if (value == null || "".equals(value)) {
              return "-";
          } else if (converter != null) {
              final String asString = converter.getAsString(FacesContext.getCurrentInstance(), component, value);
              return asString == null ? "-" : asString;
          }
  
          return String.valueOf(value);
      }
docs: Should return value string for the readonly view mode. Can be overridden
  for custom components.