You can't add a picture from your iPad's Photos because the list is blank.
or
You can't take a photo with your iPad's camera because the image is black and the shutter button doesn't work.

Resolution

To resolve these problems, you need to grant permission for the app to access your iPad Photos and camera:

1. Open your iPad's Settings app.
2. In the left pane, scroll down and tap the app name.
3. In the right pane, enable access to Photos and Camera.