If a link to a nonexistent file is found, the error no writecb in Transform class is shown

[marcospgp]

This error doesn't help figuring out what is wrong at all. For example:

<!-- build:css styles/style.min.css -->
<link rel="stylesheet" href="./style/style.css" type="text/css">
<!-- endbuild -->

in an html file, and with a nonexistent style.css file, logs "Error: no writecb in Transform class" on the console.