code: protected void addCalendarValue(Document doc, String fieldName, Object internalValue)
     {
        Calendar value = (Calendar)internalValue;
        long millis = value.getTimeInMillis();
        try
        {
           doc.add(createFieldWithoutNorms(fieldName, DateField.timeToString(millis), PropertyType.DATE));
        }
        catch (IllegalArgumentException e)
        {
           LOG.warn("'{}' is outside of supported date value range.", new Date(value.getTimeInMillis()));
        }
     }
docs: Adds the calendar value to the document as the named field. The calendar
  value is converted to an indexable string value using the
  {@link DateField} class.
  
  @param doc
  The document to which to add the field
  @param fieldName
  The name of the field to add
  @param internalValue
  The value for the field to add to the document.