Parenthood was a tough act to follow, for Erika Christensen. No doubt. But ABC’s Will Trent has been delighting the actress with its own unique mix, one of humor and “darkness.” Reflecting on her six-season run as Julia Braverman on Jason Katims’ Parenthood — which ended eight years ago January — Christensen tells TVLine, “I’m kind of an optimist to a fault, but I knew that it was a unique experience from every angle from which you could view it. “It was unique as an audience member — certainly