BUG: trying to upcast Nil (Crystal::NilType) <- NoReturn (Crystal::NoReturnType) (Exception)
  from /crystal/src/compiler/crystal/codegen/cast.cr:668:5 in 'upcast_distinct'
  from /crystal/src/compiler/crystal/codegen/cast.cr:523:15 in 'upcast'
  from /crystal/src/compiler/crystal/codegen/codegen.cr:1369:11 in 'accept'
  from /crystal/src/compiler/crystal/codegen/codegen.cr:2274:9 in 'visit'
  from /crystal/src/compiler/crystal/syntax/visitor.cr:27:12 in 'accept'
...