private Set<String> getFileReferencesInUse() {
        Set<String> fileReferencesInUse = new HashSet<>();
        for (var applicationId : listApplications()) {
            Application app = getApplication(applicationId);
            fileReferencesInUse.addAll(app.getModel().fileReferences().stream()
                                          .map(FileReference::value)
                                          .collect(Collectors.toSet()));
        }
        return fileReferencesInUse;
    }
Deletes an application and associated resources

@return true if the application was found and deleted, false if it was not present
@throws RuntimeException if deleting the application fails. This method is exception safe.
configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java