Withdrawal of petition.

If, at any time after the petition is filed, the petitioner desires to withdraw the same, he shall file with the hearing clerk (or, if filed during the course of a hearing, with the judge) a written request for permission to withdraw. The judge may, in his discretion, thereupon dismiss the petition without further procedure: Provided, That, if the request to withdraw is filed after a hearing has been opened, permission to withdraw shall be granted only in exceptional circumstances.