typing: fix failed cast when iterate over a nullable collection

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
typing: standardize error messages for AForExpr loops

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
tests: fix error messages for engine nitg-s

This follows the iterator error messages from a9986ea596189a1b3743ae0c897f2bdbb8d5e6f0

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
tests: fix test errors for engine nitc

(actually not fixing anything but putting tests away waiting for kill-nitc)

This follows the iterator error messages from a9986ea596189a1b3743ae0c897f2bdbb8d5e6f0

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
correct typo from `reciever` to `receiver` in error messages

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
nitmetrics: correct typo from `reciever` to `receiver`

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>