poetry export returns zero exit code if extras value does not exist

[l0b0]

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Arch Linux

• Poetry version: 1.1.4

• Link to your pyproject.toml file: https://github.com/linz/geospatial-data-lake/blob/95b9bc86e0df0816a3416adeb5d147f0996cf1f7/pyproject.toml

Issue

poetry export --extras="anything" prints an empty line and returns a zero exit code if the extra (in this case called "anything") does not exist. It should instead have the same result as running poetry export --extras="anything", which results in a ValueError and the message "Extra [anything] is not specified."