CSS minifying issue

[dan-online]

When going to test.css in a public directory it throws this error:

TypeError error: TypeError: Cannot read property 'length' of undefined
    at uriToSourceMapping (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/load-original-sources.js:39:38)
    at loadOriginalSources (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/load-original-sources.js:20:18)
    at /Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:26:14
    at applySourceMaps (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/apply-source-maps.js:34:5)
    at Object.callback (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:25:12)
    at doInlineImports (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:200:25)
    at inline (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:178:10)
    at fromStyles (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:151:5)
    at fromString (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:48:10)
    at doReadSources (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:33:12)
    at readSources (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/reader/read-sources.js:24:10)
    at /Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/clean.js:115:12
    at /Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/clean.js:135:34
    at minify (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/clean.js:114:35)
    at CleanCSS.minify (/Users/me/Desktop/Code/CDN-Template/node_modules/clean-css/lib/clean.js:77:12)
    at Minifier._minifyCss (/Users/me/Desktop/Code/CDN-Template/node_modules/express-minify/minifier.js:74:55)