fix: add null check to prevent API response errors (issue #13941)

.changeset/early-needles-speak.md

@@ -0,0 +1,6 @@
+---
+'integration-tests': patch
+'@aws-amplify/data-schema': patch
+---
+
+Added null check to handle potential null data in API response (issue #13941)

packages/data-schema/src/runtime/internals/operations/indexQuery.ts

@@ -189,7 +189,7 @@ function _indexQuery(
       const { data, errors } = error;
 
       // `data` is not `null`, and is not an empty object:
-      if (data !== undefined && Object.keys(data).length !== 0 && errors) {
+      if (data !== undefined && data !== null && Object.keys(data).length !== 0 && errors) {
         const [key] = Object.keys(data);
 
         if (data[key]?.items) {

packages/integration-tests/__tests__/defined-behavior/1-patterns/secondary-indexes.ts

@@ -46,6 +46,15 @@ describe('Custom secondary indexes', () => {
             },
           },
         },
+        {
+          data: null,
+          errors: [
+            {
+            path: null,
+            locations: []
+            } as any
+          ]
+          },
       ]);
       const config = await buildAmplifyConfig(schema);
       Amplify.configure(config);
@@ -70,6 +79,15 @@ describe('Custom secondary indexes', () => {
           },
         ]),
       );
+
+      // Ensuring `data: null` does not throw exception
+      // https://github.com/aws-amplify/amplify-js/issues/13941
+      expect(async () => {
+        const { data: nullDataResponse, errors: nullDataError } =
+          await client.models.Customer.listCustomerByAccountRepresentativeId({
+            accountRepresentativeId: 'YOUR_REP_ID',
+          });
+      }).not.toThrow();
     });
   });