On the site there is a tag with no value.
It can be found here:
https://e621.net/tag?name=&type=&order=name
or here:
https://e621.net/tag/show.json?id=148522
oddly, this tag is related to 27 posts
Updated by Furrin Gok
Topic: [Bug] Tag with no value
Posted under Site Bug Reports & Feature Requests
Also found in this wiki
Clicking posts just sends you to the regular posting list.
Updated by anonymous