code: protected void addBooleanValue(Document doc, String fieldName, Object internalValue)
     {
        doc.add(createFieldWithoutNorms(fieldName, internalValue.toString(), PropertyType.BOOLEAN));
     }
docs: Adds the string representation of the boolean value to the document as
  the named field.
  
  @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.