"A judge cannot decline to render judgment by reason of the silence, obscurity or insufficiency of the laws."Article 10 adds:
"It is the duty of the judge to apply the law without fear or favor. In case of doubt in the interpretation or application of the laws, it is presumed that the lawmaking body intended right and justice to prevail."So whether the judge knows what law is applicable he must render a judgment. This judgement may be based on legally sound customs, previous Court decisions, general principles of law and equity; and accepted rules of interpreting the law.
The rule is different in criminal cases. If there is no law punishing an act (or inaction) there is no crime committed. This is embedded in the legal maxim "Nullum crimen sine lege, nulla poena sine lege."
If there is no law punishing an act complained of, the judge must dismiss the case.