TypeError: Cannot set property 'path' of undefined

[BrunoQuaresma]

/var/www/node_app/node_modules/instagram-node-lib/lib/class.instagram.media.js:19
params['path'] = "/" + this.parent._api_version + "/media/popular?" + (this.parent._to_querystring(credentials));
^

TypeError: Cannot set property 'path' of undefined
at InstagramMedia.popular (/var/www/node_app/node_modules/instagram-node-lib/lib/class.instagram.media.js:19:22)
at Object. (/var/www/node_app/app.js:14:17)
at Module._compile (module.js:409:26)
at Object.Module._extensions..js (module.js:416:10)
at Module.load (module.js:343:32)
at Function.Module._load (module.js:300:12)
at Function.Module.runMain (module.js:441:10)
at startup (node.js:139:18)
at node.js:968:3

My code

Instagram.media.popular();