Sergio

It works in 0.17.0 (the error started on 0.17.1)

It seems related to zoom in tile changes: @martinRenou @ned2

This will get fixed if you update json-schema in gemspec to >= 2.5.0 per this change https://github.com/ruby-json-schema/json-schema/commit/4e84940d956052d162b89c41104158b073fdb574

You might want to look at this changeset https://github.com/sromano/fdoc/commit/70f5ac3a2aab16e007c2fe7551e9e86acc7314c1