[FW][FIX] parser: parsing empty string throws meaningful error

[fw-bot]

Description:

parse("") throws an error like cannot ready property of undefined.

Note that it doesn't cause any (known) real bug, but let's make it more robust nonetheless.

With this commit, it throws a user friendly message.

Task: : TASK_ID

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

Forward-Port-Of: #4825

[robodoo]

[fw-bot]

@LucasLefevre @rrahir cherrypicking of pull request #4825 failed.

stdout:

Auto-merging src/formulas/parser.ts
CONFLICT (content): Merge conflict in src/formulas/parser.ts
Auto-merging tests/formulas/parser.test.ts

Either perform the forward-port manually (and push to this branch, proceeding as usual) or close this PR (maybe?).

In the former case, you may want to edit this PR message as well.

⚠️ after resolving this conflict, you will need to merge it via @robodoo.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[LucasLefevre]

robodoo r+