[fbenke-pik]

Purpose of this PR

unitless is used to avoid forgetting units, but is not accepted in some projects, which actually expect an empty unit.
This PR always converts unitless in the generated submission to an empty unit.

Checklist:

• I did not use Excel to open csv files or checked that no side-effects occur (changed values, many new quotation marks, …)
• I added any renamed piam_variable to renamed_piam_variables.csv to guarantee backwards compatibility.
• For REMIND variables, I used |+| notation consistently. This can be achieved automatically with updatePlusUnit().

It is recommended to have a look at the tutorial before submission.

[merfort]

Thanks a lot, Falk!

[merfort]

@gabriel-abrahao and @flohump FYI: common definitions does not except "unitless", but enforces an empty unit cell. This is what Daniel wrote to me:

About „unitless“, this was an issue in the legacy database and a custom solution for some projects. For all submissions using the new infrastructure (i.e., ixmp4) and the new apps, please leave an empty cell in the unit column. This is consistent with an empty line in the relevant definition, see e.g. https://github.com/IAMconsortium/common-definitions/blob/22efedc13e2e459a1774d4a84e781ed028a2d639/definitions/variable/sdg-indicators/sdg.yaml#L156