The filling is missing from new CBS comedy 'Superior Donuts'

"Superior Donuts," a new CBS series based on a play by Tracy Letts, is missing one crucial ingredient: Tracy Letts.

The Pulitzer Prize winner bailed on a chance to address TV critics at our winter conference this month.

Maybe that's because the adaptation isn't very good — although it isn't terrible, either.

In the series, which debuts Thursday, Judd Hirsch plays Arthur, a cantankerous doughnut-shop owner in Chicago who has managed to stay in business for 47 years despite an aversion to selling muffins and a growing threat from higher-end chains. (Starbucks, we are led to believe, might as well be employing storm troopers as baristas.) In the opening minutes, Arthur hires an excitable young employee, Franco (Jermaine Fowler), who is inexplicably excited about dragging Arthur into the present, or at least the 20th century.

Along the way, the two bicker about such issues as gun control, race (Franco is black) and health care, as the shop's regulars interject one-liners.

"I'm not going to shoot you," a police officer (Katey Sagal) says to Franco. "I've got my body cam on."

A line like that has the potential to create friction, if not a call to the Black Lives Matter hot line, but Sagal's delivery is so affectionate the quip ends up packing about as much heat as lukewarm java.

By the end of the first episode, Arthur has warmed up to his young charge, to the point that he's willing to dig into his own pockets to bail him out of him a serious jam. So much for cantankerous.

I've never seen Letts' play, but the TV outline seems to be basically the same. Reviewing the original Broadway production, New York Times critic Charles Isherwood called it "a gentle comedy that unfolds like an extended episode of a 1970s sitcom."

That wasn't meant as a compliment. Great theater, even when going for laughs, digs deep, forcing the audience to squirm as much as laugh.

Network sitcoms don't have the time — or the guts, usually — to go that route. That explains why playwrights making the transition from stage to TV are more likely to succeed on less restrictive cable or streaming-TV dramas, as Beau Willimon has with Netflix's "House of Cards."

True, Neil Simon's "The Odd Couple" translated extremely well to the small screen in the '70s — and somewhat well in more recent times (the Matthew Perry-Thomas Lennon version is just wrapping up its third, and probably, final season on CBS). But Simon got his start writing for "Your Show of Shows" and "The Phil Silvers Show." At heart, he was always a sitcom writer, averse to long stretches without punch lines and ruffling feathers.

"Donuts" doesn't dare do each either of these things, which may make it a ratings success. But it's unlikely that Letts will be dropping by the set anytime soon.