Error which does not prevent exports: undefined method `files' for nil:NilClass (NoMethodError)

[jywarren]

This is just to track but it seems harmless with @aliciapaz's confirmation - here's the old Travis log that's exactly the same; the tests pass even though it shows this error, and the error does not disrupt the actual export:

undefined method `files' for nil:NilClass (NoMethodError)
	from /home/travis/build/publiclab/mapknitter-exporter-sinatra/vendor/.bundle/ruby/2.4.0/gems/mapknitter-exporter-1.0.9/lib/mapknitterExporter.rb:329:in `run_export'
	from /home/travis/build/publiclab/mapknitter-exporter-sinatra/app/controllers/export_controller.rb:73:in `block in run_export'
	from /home/travis/build/publiclab/mapknitter-exporter-sinatra/app/controllers/export_controller.rb:71:in `fork'
	from /home/travis/build/publiclab/mapknitter-exporter-sinatra/app/controllers/export_controller.rb:71:in `run_export'
	from /home/travis/build/publiclab/mapknitter-exporter-sinatra/app/controllers/export_controller.rb:35:in `block in <top (required)>'

Originally posted by @jywarren in #131 (comment)