fix: value 'is' or 'is not' null not working (#62)

Signed-off-by: Jim Ezesinachi <ezesinachijim@gmail.com>

packages/backend/src/execution/executors/PgExecutor/PgExecutor.test.ts

@@ -105,6 +105,54 @@ describe('PgExecutor', () => {
         ]);
     });
 
+    it('single provider is null', async () => {
+        const q = from('film')
+            .columns('film_id', 'original_language_id', 'title', 'rating')
+            .where({ original_language_id: { is: null } })
+            .take(2);
+
+        const result = await executor.execute(q, executeProps);
+
+        expect(result).toEqual([
+            {
+                film_id: 1,
+                original_language_id: null,
+                title: 'ACADEMY DINOSAUR',
+                rating: 'PG',
+            },
+            {
+                film_id: 2,
+                original_language_id: null,
+                title: 'ACE GOLDFINGER',
+                rating: 'G',
+            },
+        ]);
+    });
+
+    it('single provider is not null', async () => {
+        const q = from('customer')
+            .columns('customer_id', 'email', 'first_name', 'last_name')
+            .where({ email: { 'is not': null } })
+            .take(2);
+
+        const result = await executor.execute(q, executeProps);
+
+        expect(result).toEqual([
+            {
+                customer_id: 1,
+                email: 'MARY.SMITH@sakilacustomer.org',
+                first_name: 'MARY',
+                last_name: 'SMITH',
+            },
+            {
+                customer_id: 2,
+                email: 'PATRICIA.JOHNSON@sakilacustomer.org',
+                first_name: 'PATRICIA',
+                last_name: 'JOHNSON',
+            },
+        ]);
+    });
+
     const language = from('language')
         .columns('language_id', 'name')
         .where({

packages/backend/src/execution/executors/PgExecutor/queryBuilder/exp.ts

@@ -455,6 +455,10 @@ export class SqlBuilder {
                         `Expected value ${JSON.stringify(value)} to be a primitive in ${JSON.stringify(op)}`,
                     );
 
+                    if (value === null) {
+                        return ['op', opName, quotedColumn, ['const', null]];
+                    }
+
                     if (opName === 'in') {
                         return ['op', '= any', quotedColumn, ['param', value]];
                     }