Muller Davis, a longtime family law attorney at Davis Friedman LLP who was one of the original authors of a widely used book on family law, died Tuesday following a prolonged illness. He was 82 years old.Davis is perhaps best known in Illinois for co-authoring “The Illinois Practice of Family Law” with Jody Meyer Yazici. The book was first published in 1995.Errol Zavett, a senior counsel at Davis Friedman and Davis’ partner since 1985, described his colleague as “a pioneering light” in family …