Justification by law: good-faith acts under a factual mistake do not constitute criminal offences when genuinely believed. Nothing is an offence if done by a person who is justified by law, or who, by reason of a mistake of fact (and not a mistake of law), in good faith believes himself to be justified by law in doing it; this covers acts taken under lawful powers or rights and protects good-faith actions based on factual misapprehension.