interpret jpm "useless expression"

So I have a little problem here. I tried to run "jpm test" for a add-on I tried to develop. But every time I try to run it, it just displays

console.log: bf4c_autoloader: [JavaScript Warning: "TypeError: useless expression" {file: "resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/util/sequence.js" line: 333}]

And I have no idea where to search for this error. The only thing I found was this. So here are all files I use:

index.js (main)

var tabs = require("sdk/tabs");
var data = require("sdk/self").data;
var prefs = require("sdk/simple-prefs").prefs;

tabs.on("ready", runScript);
//tabs.open("http://battlelog.battlefield.com/bf4");
var re = /battlelog\.battlefield\.com\/bf4/;

function runScript(tab) {
    if(re.test(tab.url)){
        console.log("Found battlelog tab.");
        var worker = tab.attach({
            contentScriptFile: data.url("bf4_checker.js")
        });
        worker.port.on("sendingUsername",bf4Username)
        worker.port.on("sendingUserid",bf4Userid)
    }else{
        console.log("Looking if bf4c tab");
        var worker = tab.attach({
            contentScriptFile: data.url("bf4c_checker.js")
        });
        //see https://developer.mozilla.org/en-US/Add-ons/SDK/Guides/Content_Scripts#Communicating_with_the_add-on for further reference
        worker.port.on("bf4cCheckCallback",bf4cCheckCallback)
    }
}
function bf4cCheckCallback(m){
    //{'bf4cPage' : false,'addownAllowed':false}
    console.log(((m.bf4cPage)? 'Is a bf4c page':'Another page') + ", " + ((m.addownAllowed)? 'bf4c addon allowed!':'bf4c addon not allowed!'))
}
function bf4Username(name){
    prefs.setUsername = name;
}
function bf4Userid(id){
    prefs.setUserid =  id;
    console.log(prefs)
}

bf4_checker.js

function searchUsername(){
    if(elements = document.getElementsByClassName("username")){
        for (var i = 0; i < elements.length; i++) {
            if(elements[i].href){
                return elements[i].innerHTML;
            }
        };      
    }
    return false;
}
function searchUserid(name){
    if(elements = document.getElementsByClassName("wfont")){
        re = new RegExp('/bf4/soldier/'+name+'/stats/(\\d+)/');
        for (var i = 0; i < elements.length; i++) {
            if(typeof (result = re.exec(elements[i].href)) == 'object'){
                return (parseInt(result[1]))

            }
        }       
    }
    return false;
}
if(username = searchUsername()){
    self.port.emit('sendingUsername',username);
    if(id = searchUserid(username)){
        self.port.emit('sendingUserid',id);
    }
}
function callback(mutations) {
    var re = /(highlight)/;
    mutations.forEach(function(mutationRecord) {
        var sepe = splittedClasses(mutationRecord.target.className)
        if(mutationRecord.attributeName == "class" && sepe.indexOf('highlight') > -1 && sepe.indexOf('popover-visible') == -1 && mutationRecord.target.className != mutationRecord.oldValue){
            console.log("Got new battlereport! went from\n\t"+ mutationRecord.oldValue +"\n\t"+ mutationRecord.target.className)
        }
    });
}
function splittedClasses(className){
    var classes = className.split(" ");
    for (var i = 0; i < classes.length; i++) {
        if(classes[i] == ""){
            classes.splice(i,1);
        }
    };
    return classes;
}
if(target = document.getElementById('battlereports-icon')){
    console.log("initialized listener !")
    var observer = new MutationObserver(callback);
        observer.observe(target,{ attributes : true, attributeOldValue: true, attributeFilter : ['class'] });   
}

function metaKeyUp (event) {
    var key = event.keyCode || event.which;
    if (key == 65) {
        if(target.className != "log tools-item reports  highlight"){
            console.log("highlighted the report button");
            target.className = "log tools-item reports  highlight";
        }

    }
}
document.body.addEventListener("keyup",metaKeyUp.bind(this))

and the last one bf4c_checker.js

function isBF4CPage(){
    var header = document.getElementsByTagName("meta");
    for (var i = 0; i < header.length; i++) {
        var curr = header[i];
        if(curr.name == "x-bf4c-page"){
            return {'bf4cPage' : true,'addownAllowed': (curr.content == "true")? true : false};
        }
    }
    return {'bf4cPage' : false,'addownAllowed':false};
}
self.port.emit('bf4cCheckCallback',isBF4CPage())

Ok I was just to stupid to understand the actual purpose of jpm test, I recommend to read this articel and this one both show you how to actually use this function. So my problem was not my code it was just that it tried to do something I didn't decelerated before.