{"ast_node_type":"other","tokens":[{"end":93,"kind":"keyword","start":0,"text":"None"}]}
                None => ObligationCauseCode::BlockTailExpression(arm.body.hir_id, match_src),
                // but rather that there's a prior obligation that doesn't hold.
                Some((prior_arm_block_id, prior_arm_ty, prior_arm_span)) => {