Next.js: Preview mode breaking datocms-next-js-blog-demo

[jahlherapath]

Bug report

Describe the bug

Unhandled Runtime Error
Error: Failed to load static props

When navigating to blog post routes the following error is shown:

To Reproduce

Steps to reproduce the behavior, please provide code snippets or a repository:

1. Setup repo as per readme
2. Navigate to blog post eg. http://localhost:3000/posts/mistakes-tourists-make-on-their-first-trip-abroad

Expected behavior

Show blog page without error

System information

• OS: macOS
• Version of Next.js: 9.4.4
• Version of Node.js: 12.18.1

Additional context

If I comment out preview here it fixes the issue but can't use Preview Mode:

export async function getStaticProps({ params, preview }) {
  const data = await getPostAndMorePosts(params.slug, preview);
  const content = await markdownToHtml(data?.post?.content || "");

  return {
    props: {
      // preview,
      post: {
        ...data?.post,
        content,
      },
      morePosts: data?.morePosts,
    },
  };
}

[rokinsky]

@jahlherapath, use the default null value:

export async function getStaticProps({ params, preview = null }) {
  // ...
}

[Timer]

Closing as we confirmed the latest version of this example correctly sets the default preview value. Please ensure you have the latest version of the template.

[rokinsky]

@Timer btw, it is possible to add in the future a default value (null or false) of preview in the next.js core?