AdvAgg error

Warning: exec(): Cannot execute a blank command em advagg_ext_compress_execute_cmd() (linha 138 de /home/liconline/drupal/sites/all/modules/advagg/advagg_ext_compress/advagg_ext_compress.module).

What should I do?

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/22/feed