Null Values for image previews in response array

When querying the Shopify GraphQL Admin API at /admin/api/2024-10/graphql.json, we are seeing unexpected null values in the preview.image field within the media array.

query {
 products(query: "...", first: 100, after: "...") {
  nodes { 
    id
    media(first: 120) {
     nodes {
        preview {
          image { id url }
        }
{
    "data": {
        "products": {
            "nodes": [
                 {
                     "media":
                         "nodes": 
                            {
                                "preview": {
                                    "image": null
                                }
                            },
                            {
                                "preview": {
                                    "image": null
                                }
                            },
                            {
                                "preview": {
                                    "image": {
                                        "id": "gid://shopify/ImageSource/...",
                                        "url": "https://cdn.shopify.com/s/files/1/....jpg"
                                    }
                                }
                            },
                            {
                                "preview": {
                                    "image": null
                                }
                            }

We are receiving multiple null values for data.products.nodes.media.nodes.preview.image. Could you clarify:

  1. Is it expected behavior for some media items to have null images inside array?
  2. If so, under what conditions does this occur?
  3. If not, what could be causing this issue, and how can we ensure all media items have valid images?

Thank you for your help!

Best, Ilya