fix: allow null comparator in adhocfilter

[pkdotson]

SUMMARY

This pr fixes an issue where in the adhocfilter control null value is not allowed causing the user not able to save.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

after

Screen.Recording.2021-10-01.at.8.55.00.AM.mov

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• [x ] Has associated issue: Fixes [explore][filter] NOT EQUALS NULL doesn't allow to SAVE #16803
• 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

[suddjian]

/testenv up

[github-actions]

@suddjian Ephemeral environment spinning up at http://35.167.17.93:8080. Credentials are admin/admin. Please allow several minutes for bootstrapping and startup.

[geido]

LGTM! Thanks for the fix

[codecov]

Codecov Report

Merging #16936 (db39fbf) into master (a07c9d5) will decrease coverage by 0.04%.
The diff coverage is 82.72%.

❗ Current head db39fbf differs from pull request most recent head 8c45588. Consider uploading reports for the commit 8c45588 to get more accurate results

@@            Coverage Diff             @@
##           master   #16936      +/-   ##
==========================================
- Coverage   76.97%   76.93%   -0.05%     
==========================================
  Files        1023     1030       +7     
  Lines       54907    55024     +117     
  Branches     7486     7466      -20     
==========================================
+ Hits        42266    42333      +67     
- Misses      12393    12437      +44     
- Partials      248      254       +6     

Flag	Coverage Δ
javascript	70.92% <81.25%> (-0.12%)	⬇️

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

Impacted Files	Coverage Δ
...d/src/SqlLab/components/AceEditorWrapper/index.tsx	58.75% <ø> (ø)
...erset-frontend/src/SqlLab/components/App/index.jsx	57.14% <ø> (ø)
...tend/src/SqlLab/components/ColumnElement/index.tsx	95.45% <ø> (ø)
...qlLab/components/EstimateQueryCostButton/index.jsx	20.83% <ø> (ø)
...lLab/components/ExploreCtasResultsButton/index.jsx	7.69% <ø> (ø)
...c/SqlLab/components/ExploreResultsButton/index.jsx	92.00% <ø> (ø)
...d/src/SqlLab/components/QueryAutoRefresh/index.jsx	65.90% <ø> (ø)
...c/SqlLab/components/RunQueryActionButton/index.tsx	65.11% <ø> (ø)
...d/src/SqlLab/components/SaveDatasetModal/index.tsx	88.23% <ø> (ø)
...frontend/src/SqlLab/components/SaveQuery/index.tsx	75.55% <ø> (ø)
... and 73 more

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[zhaoyongjie]

Please hold on this PR. the NULL in the select is serialized SQL NULL. So we should generate a SQL without NULL at here.

superset/superset/connectors/sqla/models.py

Lines 713 to 737 in c577191

	def values_for_column(self, column_name: str, limit: int = 10000) -> List[Any]:
	"""Runs query against sqla to retrieve some
	sample values for the given column.
	"""
	cols = {col.column_name: col for col in self.columns}
	target_col = cols[column_name]
	tp = self.get_template_processor()
	qry = (
	select([target_col.get_sqla_col()])
	.select_from(self.get_from_clause(tp))
	.distinct()
	)
	if limit:
	qry = qry.limit(limit)
	if self.fetch_values_predicate:
	qry = qry.where(self.get_fetch_values_predicate())
	engine = self.database.get_sqla_engine()
	sql = "{}".format(qry.compile(engine, compile_kwargs={"literal_binds": True}))
	sql = self.mutate_query_from_config(sql)
	df = pd.read_sql_query(sql=sql, con=engine)
	return df[column_name].to_list()

[github-actions]

Ephemeral environment shutdown and build artifacts deleted.