One or the other validation

export default {
  name: "someDocument",
  title: "Some document",
  type: "document",
  fields: [
    {
      name: "videoUrl",
      title: "Video url",
      type: "string",
      validation: (Rule) =>
        Rule.custom((field, context) =>
          context.document.image === undefined && field === undefined
            ? "Either Video url or Image must have a value"
            : true
        ),
    },
    {
      name: "image",
      title: "Image",
      type: "image",
      validation: (Rule) =>
        Rule.custom((field, context) =>
          context.document.videoUrl === undefined && field === undefined
            ? "Either Video url or Image must have a value"
            : true
        ),
    },
  ],
};