diff --git a/.github/workflows/ci-client.yml b/.github/workflows/ci-client.yml
index 110f7f2d0..9671e14c7 100644
--- a/.github/workflows/ci-client.yml
+++ b/.github/workflows/ci-client.yml
@@ -19,3 +19,22 @@ jobs:
       - run: npm ci
       - run: npm run test
       - run: npm run lint
+
+  extension:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [14.x]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: npm
+      - run: npm ci
+      - name: install
+        working-directory: client/planning-extension
+        run: npm ci
+      - name: compile
+        working-directory: client/planning-extension
+        run: npm run compile
diff --git a/client/planning-extension/src/assignments-overview/hiddenAssignmentsList.tsx b/client/planning-extension/src/assignments-overview/hiddenAssignmentsList.tsx
index 1b4bf6b86..66d68ed8a 100644
--- a/client/planning-extension/src/assignments-overview/hiddenAssignmentsList.tsx
+++ b/client/planning-extension/src/assignments-overview/hiddenAssignmentsList.tsx
@@ -49,7 +49,7 @@ export class AssignmentsCountTracker extends React.PureComponent<{}, {loading: t
                             {menuId: 'MENU_ITEM_PLANNING_ASSIGNMENTS', badgeValue: itemsCount.toString()},
                         );
 
-                        return null;
+                        return <></>;
                     }
                 }
             </LiveAssignmentsHOC>