Missing Merge request SHA metric when commits are merged in another branch

Steps to reproduce:

1. Create a branch a-blog-post and add a commit.
2. Create a new WIP MR based for a-blog-post
3. Create a new branch b-blog-post.
4. Create a new MR based off b-blog-post.
5. Merge the MR for b-blog-post.
6. a-blog-post gets marked as merged, but it's missing the merge commit SHA:

We should probably hide that part of the widget if the information is not available?

This is what happened here:

• gitlab-com/www-gitlab-com!12962 (commits)
• gitlab-com/www-gitlab-com!12840 (commits)