feat(queries): include empty values when using "NOT" operator

[grantfitzsimmons]

Fixes part of #6446

Screenshots and examples below are based on a local copy of the sbmnhiz database used for developing an export workflow for their institution.

In this example, the main query filter is on the EnvironmentalProtectionStatus in the Determination table. In this case, we want to return all Collection Object records where EnvironmentalProtectionStatus does NOT contain the word 'endangered'. In the current release (v7.11.2.1), the not operator causes Specify to ignore blank/null values as well, which is not intuitive and does not match the preferable behavior used in Specify 6.

Left: issue-6446 (this PR), Right: v7.11.2.1

The query built in Specify 6 is as follows:

select
  count(*) as col_0_0_
from
  collectionobject collection0_
  left outer join determination determinat1_ on collection0_.CollectionObjectID = determinat1_.CollectionObjectID
  left outer join taxon taxon2_ on determinat1_.TaxonID = taxon2_.TaxonID
  left outer join taxon taxon3_ on determinat1_.PreferredTaxonID = taxon3_.TaxonID
  left outer join collectingevent collecting4_ on collection0_.CollectingEventID = collecting4_.CollectingEventID
  left outer join locality locality5_ on collecting4_.LocalityID = locality5_.LocalityID
  left outer join geography geography6_ on locality5_.GeographyID = geography6_.GeographyID
  left outer join localitydetail localityde7_ on locality5_.LocalityID = localityde7_.LocalityID
where
  (
    determinat1_.IsCurrent = 1
    or determinat1_.IsCurrent is null
  )
  and (
    taxon2_.EnvironmentalProtectionStatus not like '%endangered%'
    or taxon2_.EnvironmentalProtectionStatus is null
  )
  and taxon3_.Text2 = 'Published name'
  and collection0_.CollectionMemberID = 4

Critically, this PR aims to match the behavior or {field}.{table} is null akin to Specify 6.

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add relevant issue to release milestone
• Add pr to documentation list
• Add automated tests
• Add a reverse migration if a migration is present in the PR

Testing instructions

• Create a query with a field using the "NOT" operator with "In", "Contains", or "Equals" on a field that has empty/NULL data (e.g., NOT Equals "some value").
• Execute the query and check that empty/NULL records are included in results and count.
• Test on v7.11.2.1 to confirm empty/NULL records were excluded before the fix.

[Copilot]

Pull Request Overview

This PR updates the query filtering behavior to include NULL/empty values when using the "NOT" operator, aligning Specify 7 with the historical Specify 6 behavior and user expectations. When applying negated filters, the system now explicitly includes records where the filtered field is NULL or empty.

Key Changes

• Added null_safe_not() helper function to handle negated predicates with NULL value inclusion
• Modified query filter application logic to use the new helper when negate is True
• Preserved existing behavior for non-negated filters

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[emenslin]

• Create a query with a field using the "NOT" operator with "In", "Contains", or "Equals" on a field that has empty/NULL data (e.g., NOT Equals "some value").
• Execute the query and check that empty/NULL records are included in results and count.
• Test on v7.11.2.1 to confirm empty/NULL records were excluded before the fix.

Looks good!

[Iwantexpresso]

• Create a query with a field using the "NOT" operator with "In", "Contains", or "Equals" on a field that has empty/NULL data (e.g., NOT Equals "some value").

• Execute the query and check that empty/NULL records are included in results and count.

• Test on v7.11.2.1 to confirm empty/NULL records were excluded before the fix.

No issues found! The Le left image is the current pr and the right image is the test on v7.11.2.1

Query used

It looks good to me!