nl_tokens: checks if model file exists requires it and returns it .
pl_tokens: function requireModel ( filePath , cb ) { //check if file exist. if not return error fs . exists ( filePath , function ( exists ) { if ( ! exists ) { return cb ( new Error ( "Requested Model Not Found!" ) ) ; } libProduct . <mask> = require ( filePath ) ; return cb ( null , libProduct ) ; } ) ; }