fix: subqueryIn null values used "__null__" instead of NULL_SENTINEL

client.ts stored null subquery values as "__null__" but SubqueryInOperator
matches with NULL_SENTINEL — null values silently never matched.
Also fixed same pattern in index.ts partition grouping for consistency.

Author: teamchong

src/client.ts

@@ -15,6 +15,7 @@ import type {
   VectorSearchParams,
   WindowSpec,
 } from "./types.js";
+import { NULL_SENTINEL } from "./types.js";
 import type { Operator, RowBatch } from "./operators.js";
 import { rowPassesFilters } from "./decode.js";
 import { computePartialAgg, finalizePartialAgg } from "./partial-agg.js";
@@ -466,7 +467,7 @@ export class DataFrame<T extends Row = Row> {
           const col = cols[0];
           if (col) {
             const val = row[col];
-            valueSet.add(val === null ? "__null__" : typeof val === "bigint" ? val.toString() : String(val));
+            valueSet.add(val === null || val === undefined ? NULL_SENTINEL : typeof val === "bigint" ? val.toString() : String(val));
           }
         }
         resolved.push({ column: deferred.column, valueSet });

src/index.ts

@@ -1,6 +1,7 @@
 import { DataFrame, TableQuery } from "./client.js";
 import type { QueryDescriptor, QueryExecutor } from "./client.js";
 import type { AppendOptions, AppendResult, DropResult, ExplainResult, QueryResult, Row, QueryDORpc, MasterDORpc } from "./types.js";
+import { NULL_SENTINEL } from "./types.js";
 import { LocalExecutor } from "./local-executor.js";
 import { createFromJSON, createFromCSV, createDemo } from "./convenience.js";
 import { sqlToDescriptor, buildSqlDataFrame } from "./sql/index.js";
@@ -207,7 +208,7 @@ class RemoteExecutor implements QueryExecutor {
       const partCol = options.partitionBy;
       const groups = new Map<string, Record<string, unknown>[]>();
       for (const row of rows) {
-        const key = row[partCol] === null || row[partCol] === undefined ? "__null__" : String(row[partCol]);
+        const key = row[partCol] === null || row[partCol] === undefined ? NULL_SENTINEL : String(row[partCol]);
         let group = groups.get(key);
         if (!group) { group = []; groups.set(key, group); }
         group.push(row);