Exception when the site is under a subdirectory and has a base url different from /

Problem/Motivation

There's an exception when the site is under a subdirectory and has a base url different from /

UnexpectedValueException: External URLs do not have internal route parameters. in Drupal\Core\Url->getRouteParameters() (line 583 of .../web/core/lib/Drupal/Core/Url.php).

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes