Currently, it is possible to have two documents with same name in one ticket, that means it isn't possible to access any of them - Tracker doesn't know which one to return. On an attempt to add document with name that's already taken, Tracker should return an error message.
When adding a document to a ticket, check that a name is not already taken, and error out if it is.
Student is expected to send a patch for wikimedia-cz/tracker repository, hosted at Wikimedia Gerrit. When claiming task on GCI website, student should claim a respective Phabricator task as well.