If the obligor asserts as a defense that he is not the father of the child for whom support is sought and it appears to the court that the defense is not frivolous and if both of the parties are present at the hearing or if the proof required in the case indicates that the presence of either or both of the parties is not necessary, the court may adjudicate, by a jury trial if demanded by either party, the paternity issue. Otherwise the court may continue the hearing until the paternity issue has been adjudicated.