Here's the returned PreviewData

{
  "previewData": {},
  "props": {
    "preview": false,
    "path": "/*",
    "*": "preview",
    "uri": "/",
    "location": {
      "pathname": "/preview/",
      "search": "",
      "hash": ""
    },
    "pageContext": {
      "matchPath": "/preview/*"
    },
    "params": {},
    "pathContext": {
      "matchPath": "/preview/*"
    }
  }
}