fix(sql-lab): do not replace undefined schema with empty object

[villebro]

SUMMARY

In a change introduced in #18609, SQL Lab incorrectly replaces a missing schema with an empty object when dispatching the query action, which causes the query to fail in the backend, which later breaks the whole UI and makes it impossible to enter SQL Lab again.

See a few examples of what a valid schema is in this context:

superset/superset-frontend/src/SqlLab/components/SqlEditorLeftBar/index.tsx

Line 42 in 3a231f6

queryEditorSetSchema: (queryEditor: QueryEditor, schema?: string) => void;

superset/superset-frontend/src/components/DatabaseSelector/index.tsx

Line 96 in 3a231f6

onSchemaChange?: (schema?: string) => void;

superset/superset-frontend/src/components/DatabaseSelector/index.tsx

Line 99 in 3a231f6

schema?: string;

AFTER

Now SQL Lab executes correctly even when not selecting a schema:

BEFORE

Previously the schema would fail to execute due to the empty object not being compatible with the column type in the metastore:

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue: closes DB Engine error 1.5.0rc2  #19658
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[zhaoyongjie]

LGTM

[codecov]

Codecov Report

Merging #19664 (f3f70e2) into master (3a231f6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #19664   +/-   ##
=======================================
  Coverage   66.47%   66.47%           
=======================================
  Files        1681     1681           
  Lines       64467    64467           
  Branches     6607     6607           
=======================================
  Hits        42856    42856           
  Misses      19917    19917           
  Partials     1694     1694           

Flag	Coverage Δ
javascript	51.14% <ø> (ø)

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

Impacted Files	Coverage Δ
superset-frontend/src/SqlLab/actions/sqlLab.js	60.39% <ø> (ø)

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[kgabryje]

lgtm!