Cssmin not minifying css files

Hi everyone, I'm trying to join some css files to apply the Cssmin filter, this is the snippet

$this->assets
            ->collection('styles')
            ->setTargetPath('css/common.min.css')
            ->setTargetUri("css/common.min.css?v={$this->version}")
            ->AddCss('css/styles.css', true, true)
            ->join(true)
            ->addFilter(
                new \Phalcon\Assets\Filters\Cssmin()
            );

I'm running php 7.2 on CentOs 7. For some reason, if I try to minify the css, I get an error page: https://postimg.cc/v1qzDV66 But if I just remove the minification filter it works just fine, I enabled php errors, and I got nothing. On the apache error logs I got this: [Tue Nov 06 11:47:10.309265 2018] [core:notice] [pid 13071:tid 140264820119680] AH00052: child pid 16449 exit signal Segmentation fault (11)

Does Cssmin require any library? I can't find a list of requirements.