Steps to reproduce:

1. Log in to back office.
2. Go to Content / Content structure.
3. Start creating a new content 'Tag'.

Actual result:

See attached screenshots.

Cannot create a new Tag content because of an error 500 occurred.

An exception has been thrown during the rendering of a template ("More than one result was found for query although one row or none was expected.").

Expected result:

Tag content can be created without any exceptions.