Ember-cli 2.7.0 -- warning app/tests.map missing

[workmanw]

After upgrading to ember-cli 2.7.0 (from 2.5.0) I started receiving this warning when running ember serve:

Warning: ignoring input sourcemap for app/tests.js because ENOENT: no such file or directory, open '/Users/wesley/tmp/source-map-test/tmp/source_map_concat-input_base_path-sqblxX3C.tmp/0/app/tests.map'

I reduce the warning down to this addon. It's very easy to reproduce using ember-cli version 2.7.0. Here are steps:

ember new source-map-test
cd source-map-test
ember serve 
# works fine. no warning. #

ember install ember-cli-blanket
ember serve
# receive warning about missing map. #