§1. A petitioner or respondent who is absent from the trial and has not given proof of a just impediment is obliged both to pay the expenses of the litigation which have accrued because of the absence and to indemnify the other party if necessary.
§2. If both the petitioner and the respondent were absent from the trial, they are obliged in solidum to pay the expenses of the litigation.
Source: Code of Canon Law (Vatican.va)