Cannot find module 'less' though less is present - less

Question

I know this question had been asked a few times already, but I tried everything I found and nothing worked, so I'll ask directly
I have a symfony 2.0 project, in which I'm building a docker
But when I try to run assetic:dump, I get this error :
[RuntimeException]
module.js:340
throw err;
^
Error: Cannot find module 'less'
at Function.Module._resolveFilename (module.js:338:15)
at Function.Module._load (module.js:280:25)
at Module.require (module.js:364:17)
at require (module.js:380:17)
at Object.<anonymous> (/tmp/assetic_lessJknvfV:1:74)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
But less is already installed, when I type which less :
/usr/bin/less
When I type /usr/bin/less it works
My parameters.ini less part :
less.node = /usr/bin/nodejs
less.node_path = /usr/bin/less
My assetic config in config.yml :
assetic:
debug: %kernel.debug%
use_controller: false
filters:
cssrewrite: ~
less:
node: %less.node%
node_paths: [%less.node_path%]
apply_to: "\.less$"
yui_css:
jar: %kernel.root_dir%/Resources/java/yuicompressor-2.4.7.jar
yui_js:
jar: %kernel.root_dir%/Resources/java/yuicompressor-2.4.7.jar
I'm working with php 5.6
Thanks for your time and help :)