Error with 'karma start'

[bobmyers]

~/wrk/es6-playground $ karma start
INFO [karma]: Karma v0.12.24 server started at http://localhost:9876/
INFO [launcher]: Starting browser Chrome
ERROR [karma]: [TypeError: Cannot call method 'forEach' of undefined]
TypeError: Cannot call method 'forEach' of undefined
    at C:\cygwin64\home\Bob\wrk\es6-playground\node_modules\karma-traceur-preprocessor\index.js:25:19
    at nextPreprocessor (C:\cygwin64\home\Bob\wrk\es6-playground\node_modules\karma\lib\preprocessor.js:58:2\
8)
    at C:\cygwin64\home\Bob\wrk\es6-playground\node_modules\karma\lib\preprocessor.js:97:7
    at fs.js:266:14
    at C:\cygwin64\home\Bob\wrk\es6-playground\node_modules\karma\node_modules\graceful-fs\graceful-fs.js:10\
4:5
    at Object.oncomplete (fs.js:107:15)