fix(event-flow-viz): handle null metadata selection

[maloun96]

SUMMARY

Fix issue when removing additional metadata from the event flow chart. This was caused by the server that returns 500.
To fix that we need to send an empty array instead of null for multiselects.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before

After

TEST PLAN

1. Log In
2. Create a new event flow chart
3. Add additional metadata
4. Run Query
5. Remove all additional metadata

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API
• Fix [chart]event flow chart is broken after removing additional meta data  #11746

[codecov-io]

Codecov Report

Merging #11885 (fb69383) into master (4666445) will decrease coverage by 12.24%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master   #11885       +/-   ##
===========================================
- Coverage   67.12%   54.88%   -12.25%     
===========================================
  Files         915      421      -494     
  Lines       44537    14809    -29728     
  Branches     4235     3822      -413     
===========================================
- Hits        29897     8128    -21769     
+ Misses      14526     6681     -7845     
+ Partials      114        0      -114     

Flag	Coverage Δ
cypress	54.88% <100.00%> (+3.27%)	⬆️
javascript	?
python	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../src/explore/components/controls/SelectControl.jsx	87.50% <100.00%> (-5.90%)	⬇️
...uperset-frontend/src/dashboard/util/dnd-reorder.js	0.00% <0.00%> (-100.00%)	⬇️
...rset-frontend/src/dashboard/util/getEmptyLayout.js	0.00% <0.00%> (-100.00%)	⬇️
...dashboard/components/resizable/ResizableHandle.jsx	0.00% <0.00%> (-100.00%)	⬇️
.../src/dashboard/util/getFilterScopeFromNodesTree.js	0.00% <0.00%> (-93.48%)	⬇️
...src/dashboard/components/gridComponents/Header.jsx	10.52% <0.00%> (-86.85%)	⬇️
...rc/dashboard/components/gridComponents/Divider.jsx	13.33% <0.00%> (-86.67%)	⬇️
...ontend/src/dashboard/util/getDashboardFilterKey.ts	14.28% <0.00%> (-85.72%)	⬇️
...nd/src/views/CRUD/data/query/QueryPreviewModal.tsx	14.70% <0.00%> (-82.97%)	⬇️
...set-frontend/src/views/CRUD/welcome/EmptyState.tsx	5.71% <0.00%> (-82.10%)	⬇️
... and 787 more

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[villebro]

I think it might be simpler to make the backend more resilient to nulls by changing the below, something like for col in form_data["all_columns"] or []:
https://github.com/apache/incubator-superset/blob/07288789e2adce50939eeb564b1771120bfbc11d/superset/viz.py#L2701

[junlincc]

Thanks for the quick fix!

unrelated to this PR

@rusackas can we change metadata back to additional metadata?

[maloun96]

@junlincc should we change as @villebro said or left from the front-end this fix?

[rusackas]

Thanks for the quick fix!

unrelated to this PR

@rusackas can we change metadata back to additional metadata?

Already done.

[rusackas]

@junlincc should we change as @villebro said or left from the front-end this fix?

I'd say go ahead and make the change as he suggested... might as well get it here and now :D Then it's fixed on F/E and B/E 🎉

[villebro]

I agree with @rusackas , better to make both ends more resilient.

[villebro]

One more thing - I might be missing something here, but I don't quite get why this can't always be initialized to []. @maloun96 can you check if that works? I'd much rather not have a ternary here that can be avoided.

[maloun96]

@villebro in case that select has only 1 value it should be initialized with null, only if it can have multiple select that it should be []