fix: skip row if created_at_fk is null

[eschutho]

Some migrations are failing for ffa79af61a56 when a created_by_fk is blank for a dataset. This PR skips that row if null

TESTING INSTRUCTIONS

TBD

ADDITIONAL INFORMATION

• Has associated issue:
• 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

[eschutho]

@john-bodley this should fix the issue that @AAfghahi was reporting on #20617. I'm trying to get a test if possible, but I was able to test this locally.

[codecov]

Codecov Report

Merging #20939 (fc55ac3) into master (ac58582) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #20939   +/-   ##
=======================================
  Coverage   66.38%   66.38%           
=======================================
  Files        1766     1766           
  Lines       67225    67225           
  Branches     7135     7135           
=======================================
  Hits        44626    44626           
  Misses      20774    20774           
  Partials     1825     1825           

Flag	Coverage Δ
hive	53.20% <ø> (ø)
mysql	81.02% <ø> (ø)
postgres	81.09% <ø> (ø)
presto	53.10% <ø> (ø)
python	81.56% <ø> (ø)
sqlite	79.67% <ø> (ø)
unit	50.52% <ø> (ø)

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

Impacted Files	Coverage Δ
superset/views/sql_lab.py	60.52% <0.00%> (ø)

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[ktmud]

Thanks for the fix!

[eschutho]

I'm going to merge this without a test, and I'm looking into a longer-term solution around alembic migration tests, possibly https://pypi.org/project/pytest-alembic/