On Wikivoyage wikis it's common to configure mapframes using templates or modules so that they try to display all commonly used groups even if they are empty. This behavior leads to the vast majority of logspam in the kartotherian logs when the requested groups are empty.
Received failed group: Error: Received empty response for group "Ausgehen"
Note, that the Received empty response for group error originates from the mapdata lib and is forwarded to kartotherian where it's logged. Let's not trigger/log these warnings, when the group is named. The cases relevant to us are these where the group id is a hash.
See also https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Kartographer/+/834353/