Fix behavior of null in IN and NOT IN operators with empty sets

[Copilot]

This PR fixes the issue where SELECT null IN () and SELECT null NOT IN () were returning NULL instead of the expected false and true values respectively.

Changes Made

• Fixed Expression Compiler (src/50expression.js):

  • Added a skipNullCheck flag to the expression compilation logic
  • When the right side of IN/NOT IN is an empty array, the flag bypasses null-checking logic since the result is deterministic
  • For empty arrays: IN () always returns false (nothing is in an empty set), NOT IN () always returns true (everything is not in an empty set)
  • This follows SQL standard behavior where operations on empty sets have deterministic results regardless of null operands

• Added Test Case (test/test1529.js):

  • Tests that null IN () returns false
  • Tests that null NOT IN () returns true
  • Verifies non-null values still work correctly with empty sets

Testing

• ✅ All new tests pass
• ✅ Existing IN/NOT IN operator tests still pass (test248.js, test024.js, test053.js)
• ✅ Build process completes successfully
• ✅ No security vulnerabilities introduced (CodeQL analysis clean)

The fix is minimal and surgical, only affecting the specific case of empty arrays in IN/NOT IN operators with null operands, while preserving all existing behavior for non-empty sets and non-null operands.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>SELECT null [not] IN ()</issue_title>
<issue_description>Derived from https://github.com/AlaSQL/alasql-sqllogictest/blob/a10ff82e75edafae2ce96c9d02ab47cfc85d4507/results/output.md#1620-testevidencein1test

---

SELECT null IN ()

Expected: false but got NULL

---

SELECT null NOT IN ()

Expected: true but got NULL

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes SELECT null [not] IN () #1529

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[mathiasrw]

@copilot Continue

[Copilot]

@copilot Continue

I've implemented the fix for the null IN/NOT IN empty set issue. The changes are in commit 4135361.

The fix ensures that:

• SELECT null IN () returns false (nothing is in an empty set)
• SELECT null NOT IN () returns true (everything is not in an empty set)

This is achieved by adding a skipNullCheck flag that bypasses the null-checking logic when the IN/NOT IN operator has an empty array on the right side, since the result is deterministic regardless of whether the left operand is null.