Adding value of item to source values in a custom attribute type for 'frontend/..'

[caguilarAventi]

Hi, Magento community right now I working in the new template for Magento 2.X when I tried to compile the files less I get one error about this file styles-l.less.

The theme.xml

<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
    <title>Aventi ticket</title>
    <parent>Magento/blank</parent>
    <media>
        <preview_image>media/preview.jpg</preview_image>
    </media>
</theme>

Define theme

module.exports = {
    aventi: {
        area: 'frontend',
        name: 'Aventi/ticket',
        locale: 'en_US',
        files: [
            'css/styles-m',
            'css/styles-l'
        ],
        dsl: 'less'
   

Any idea why this error can be?