[WorldMap] Add required parameter validation

[graceguo-supercat]

If user didn't set bubble size, chart will throw confusing error message.

@michellethomas @mistercrunch

[codecov-io]

Codecov Report

Merging #4922 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4922   +/-   ##
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  Coverage   77.12%   77.12%           
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  Files          44       44           
  Lines        8539     8539           
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  Hits         6586     6586           
  Misses       1953     1953

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[michellethomas]

good find!

[mistercrunch]

The original intent was to make this optional though, we didn't want to force the user to layer a bubble on top of the color area

[mistercrunch]

The fix probably should be to make the metric optional on the backend

[graceguo-supercat]

yeah, i am thinking about this could be optional parameter.
Here:
qry['metrics'] = [
self.form_data['metric'], self.form_data['secondary_metric']]

I don't know what's the best way to fallback a default value? Otherwise it will append None into metrics array

[mistercrunch]

The changes on MetricsControl introduced some issues I'm addressing here: #4914

[graceguo-supercat]

ok I will close this PR and just verify World Map viz after you merged #4914.