FWIW I have proposed a patch on Ubuntu and upstream: https://github.com/composer/class-map-generator/pull/31
which fixes this bug
- Bug#1129019: php-composer-class-map-generator: 1.7.1-1 FTBFS... Renan Rodrigo
- Bug#1129019: 1.7.1-1 FTBFS on Ubuntu resolute-proposed ... Renan Rodrigo
