fix: Friendly error messages for null and undefined values inside message files (#1041)

Co-authored-by: windmillcode0 <michaelodumosu57@gmail.com>

packages/i18n/src/__tests__/build.test.ts

@@ -161,4 +161,17 @@ describe('Built Tools', () => {
     );
     expect(mockWriteFile).toBeCalledWith('output.d.ts', expectedDts, 'utf8');
   });
+
+  it('should throw an error if messages file contains null or undefined', async () => {
+    const invalidFileContent = stringifyYAML({
+      simple: 'example',
+      invalidField: null,
+    });
+
+    mockReadFile.mockResolvedValue(invalidFileContent);
+
+    await expect(parseMessagesFile('invalid.yml')).rejects.toThrowError(
+      'Messages file should not contain `null` (found at "invalidField")',
+    );
+  });
 });

packages/i18n/src/build.ts

@@ -166,6 +166,11 @@ function _parseMessagesObject(
       ];
     }
     case 'object':
+      if ([null, undefined].includes(object)) {
+        throw new Error(
+          `Messages file should not contain \`${object}\` (found at "${path.join('.')}")`,
+        );
+      }
       if (Array.isArray(object))
         return object.flatMap((item, i) =>
           _parseMessagesObject(path.concat(String(i)), item, depth + 1),