[Bug] Fix inconsistent return types in selector values

[huong-li-nguyen]

Description

Previously if you've specified the options of a selector as a List[Dict] inside a Parameter, the value was returned as a List[Dict] when "ALL" was selected (introduced by us), but would return a List of values only when selecting other values from the multi selector (dash default). This could lead to issues when using custom charts, as it's not immediately transparent for the user what the return type is, see #557.

• Fixes inconsistent return types in selectors by always returning a List (similar to Dash)

FYI: @lingyielia @petar-qb @antonymilne

Screenshot

Notice

• I acknowledge and agree that, by checking this box and clicking "Submit Pull Request":

  • I submit this contribution under the Apache 2.0 license and represent that I am entitled to do so on behalf of myself, my employer, or relevant third parties, as applicable.
  • I certify that (a) this contribution is my original creation and/or (b) to the extent it is not my original creation, I am authorized to submit this contribution on behalf of the original creator(s) or their licensees.
  • I certify that the use of this contribution as authorized by the Apache 2.0 license does not violate the intellectual property rights of anyone else.
  • I have not directly or indirectly referenced individuals, products or companies in any commits.
  • I have not added data or restricted code in any commits, directly or indirectly.

[lingyielia]

Thanks Li! I agree with should follow Dash default in this case. Approved with 2 comments.

[antonymilne]

Amazing work all round @GiulioMorinaQB for the great bug report and @lingyielia and @huong-li-nguyen for the very speedy temporary and permanent fix! 💯

Just to check: @huong-li-nguyen does the new test fail before your fix?

[huong-li-nguyen]

Just to check: @huong-li-nguyen does the new test fail before your fix?

Yes, of course! That's how I checked that the test was working 😄