Three JS TypeError: url is undefined

i'm new at three js and i'm trying to clone some object using obj + mtl format. The problem is when i'm loading my object i have an TypeError: url is undefined in three.js files.

var models = {
    fence : {
        obj: "http://localhost:8000/SIA/src/medias/models/gltf/fence/Fence.obj",
        mlt: "http://localhost:8000/SIA/src/medias/models/gltf/fence/Fence.mlt",
        mesh: null
    },
    grass : {
        obj : "http://localhost:8000/SIA/src/medias/models/gltf/grass/Grass.obj",
        mlt: "http://localhost:8000/SIA/src/medias/models/gltf/grass/Grass.mlt",
        mesh: null
    }
};
//Meshes index
var meshes = {}; 

And this is how i get my url :

  for( var _key in models ){
        (function(key){ 

            mtlLoader.load(models[key].mtl, function(materials){
            materials.preload();

                objLoader.setMaterials(materials);
                objLoader.load(models[key].obj, function(mesh){

                    mesh.traverse(function(node){
                        if( node instanceof THREE.Mesh ){
                            node.castShadow = true;
                            node.receiveShadow = true;
                        }
                    });
                    models[key].mesh = mesh;

                });
            });

        })(_key);
    }

I guess it's mtlLoader the problem, but i'm not sure. I just use console.log(""); to find where the code stop. I checked my models url 10 times and they are correct. If anyone can help me to find where is the mistake.