How to Use agent.add() to Return Image Messages in Dialogflow Fulfillment?

Question

In Dialogflow (ES) fulfillment, how can I use agent.add() to return an image message, and what is the correct format for it?

I've tried to return an image using agent.add() like I did with a Card, but it doesn't seem to work. When I use the following code:

agent.add(new Image({
  imageUri: "https://reactnative.dev/img/tiny_logo.png"
}));

The fulfillment message I receive is empty:

"fulfillmentMessages": [
  {
    "text": {
      "text": [
        ""
      ]
    }
  }
]

What is the correct way to return an image message using agent.add() in Dialogflow?