How to do assertJson validation on array elements that can sometimes be empty?

I have API response:

[
  {
    "title": "title",
    "gallery": [
      {
        "src": "fsdg.jpg"
      }
    ]
  },
  {
    "title": "title2",
    "gallery": null
  }
]

In my test, I want to test each type of element. Here is my code:

            ->assertJson(fn (AssertableJson $json) =>
                $json->whereAllType([
                        '0.title' => 'string',
                        '0.gallery' => 'array|null',
                        '0.gallery.0.src' => 'string'
                    ])
            );

But I'm getting an error: Property [0.gallery.0.src] does not exist. Failed asserting that false is true.

I understand the meaning of the error, but please help me how do I check the properties inside an array(gallery) that may be empty (nullable)?