StringField field = extractField();
StringField field = extractField(dd);
    private void parseBody(DataDictionary dd) throws InvalidMessage {        StringField field = extractField();        while (field != null) {            if (isTrailerField(field.getField())) {                pushBack(field);                return;            }            if (isHeaderField(field.getField())) {                if (isValidStructure) {                    isValidStructureTag = field.getField();                    isValidStructure = false;                }                header.setField(field);            } else {                setField(field);            }            // Group case            if (dd != null && dd.isGroup(getMsgType(), field.getField())) {                parseGroup(field, dd, this);            }            field = extractField();        }    }