[ybai08]

SQLite never calls xStep for an aggregate over an empty input; it only calls xFinal. create_aggregate initializes the JavaScript state inside the step wrapper, so on an empty input finalize receives undefined instead of the value returned by init:

db.create_aggregate("json_agg", {
    init: () => [],
    step: (state, val) => [...state, val],
    finalize: (state) => JSON.stringify(state),
});
db.exec("SELECT json_agg(x) FROM (SELECT 1 AS x WHERE 0)"); // NULL, expected '[]'

db.create_aggregate("count_rows", { init: () => 0, step: (s, v) => s + 1 });
db.exec("SELECT count_rows(x) FROM (SELECT 1 AS x WHERE 0)"); // NULL, expected 0

A finalize that reads properties of its state (for example state.vals.length with init: () => ({ vals: [] })) throws a TypeError on empty input, so the whole query fails.

The finalize wrapper now calls init when no state exists for the aggregate context yet, so finalize (or the default identity finalize) always receives an initialized state. Aggregates without init still return NULL on empty input, since the default init returns null.

Tests: added cases to test/test_aggregate_functions.js for an empty input with init + finalize, with init only, and without init.

Testing note: Emscripten is not installed on the machine this was prepared on, so the bundles were not rebuilt with npm run build. Instead, the src/api.js text inside the published 1.15.0 debug bundles (sql-wasm-debug.js, sql-wasm-inline-debug.js; identical to src/api.js at 2824d38) was replaced with the patched file (rebased on #640), and the test runner was run against those:

• before the fix: node test/all.js wasm and node test/all.js wasm-debug -> FAIL test aggregate_functions ("Aggregate over no rows finalizes the value returned by init: null !== '[]'"), Passed:24 Failed:1
• after the fix: node test/all.js wasm-debug and node test/all.js wasm-inline-debug -> Passed:25 Failed:0
• npx eslint . passes; node test/builds.js passes

The optimized wasm, wasm-browser and wasm-inline bundles were not rebuilt, so the full npm test was not run with the change.

[lovasoa]

Thank you 👍