fix indexed column EqFilter condition for is null operator

src/tests/simple-queries.spec.ts

@@ -502,5 +502,16 @@ describe('Simple queries', () => {
             members               VARCHAR[]
         );`);
         expectQueryError(() => none(`INSERT INTO example (members) VALUES (ARRAY[])`), /cannot determine type of empty array/);
-    })
+    });
+
+    it('should select row with null value condition for indexed column', async () => {
+        none(`
+            CREATE TABLE "tableA" ("id" SERIAL NOT NULL, "reference" INTEGER);
+            CREATE INDEX "IDX_1" ON "tableA" ("reference");
+            INSERT INTO "tableA"(id, reference) values (1, null);
+            `);
+        // it is important that EqFilter hasItem gets called, so two same conditions are applied to fall both into best and sorted conditions
+        const got = many(`SELECT "tableA"."id" FROM "tableA" WHERE ("tableA"."id" IN (1, 2) AND "tableA"."reference" IS NULL) AND ("tableA"."id" IN (1, 2) AND "tableA"."reference" IS NULL)`);
+        expect(got).toHaveLength(1);
+    });
 });

src/transforms/eq-filter.ts

@@ -28,15 +28,20 @@ export class EqFilter extends FilterBase {
     }
 
     hasItem(item: Row, t: _Transaction) {
+        const isEq = this.op === 'eq';
         const val = this.onValue.get(item, t);
+
+        if (this.matchNull && nullIsh(val)) {
+            return isEq;
+        }
         if (nullIsh(val)) {
             return false;
         }
         const eq = this.onValue.type.equals(val, this.equalsCst);
         if (nullIsh(eq)) {
             return false;
         }
-        return this.op === 'eq' ? !!eq : !eq;
+        return isEq ? !!eq : !eq;
     }
 
     constructor(private onValue: IValue