ember-changeset error when executing the tests

When trying to execute the tests on the ember addon ember-changeset I get the following error:

MacBook-Pro-4:ember-changeset lukas$ ember test
Path must be a string. Received null
TypeError: Path must be a string. Received null
   at assertPath (path.js:7:11)
   at Object.join (path.js:1211:7)
   at CoreObject.<anonymous> (/usr/local/lib/node_modules/ember-cli/lib/models/addon-discovery.js:117:26)
   at Array.map (native)
   at CoreObject.discoverFromDependencies (/usr/local/lib/node_modules/ember-cli/lib/models/addon-discovery.js:107:70)
   at CoreObject.discoverChildAddons (/usr/local/lib/node_modules/ember-cli/lib/models/addon-discovery.js:69:33)
   at CoreObject.discoverAddons (/usr/local/lib/node_modules/ember-cli/lib/models/addon.js:209:42)
   at CoreObject.initializeAddons (/usr/local/lib/node_modules/ember-cli/lib/models/addon.js:222:10)
   at setupRegistryForEachAddon (/usr/local/lib/node_modules/ember-cli/node_modules/ember-cli-preprocess-registry/preprocessors.js:18:10)
   at Object.module.exports.setupRegistry (/usr/local/lib/node_modules/ember-cli/node_modules/ember-cli-preprocess-registry/preprocessors.js:46:3)

I looked trough the source code but couldn't find the error. Any ideas? Thanks for the help!