async：无法读取未定义的属性“map”

Question

我有一个async.map的函数，它一直工作到地图的回调然后我得到这个错误：

function findSolutionsOneWay(tw, urls, isOutbound, callback){

    async.map(urls, function(url, next) {

        getRailFeed(url, function(err, responseJson){
            if(err)
            {
                console.log(TAG + '@findSolutionsOneWay, err: ' + err);
                console.log(TAG + '@findSolutionsOneWay, url: ' + url);
                return next(null, ''); // donT break
            }
            //success
            return next(null, responseJson);
        });
    },
    // async callback
    function(err, listResponseJson){
        if(err){
            console.log(TAG + '@findSolutionsOneWay failed: ' + aReq.toString());
            return callback(err);
        }

        console.log(TAG + '@findSolutionsOneWay, isOutbound ' + isOutbound);
        console.log(TAG + '@findSolutionsOneWay, listResponseJson size ' + listResponseJson.length);

        var oneWaySolutions = [];
        for(var i=0; i<listResponseJson.length; i++){
            console.log(TAG + '@findSolutionsOneWay,  # # # # # # processing response # : '+ i);
            evaluateOneWaySolutions(JSON.parse(listResponseJson[i]), oneWaySolutions, isOutbound, tw);
        }

        console.log(TAG + '@findSolutionsOneWay, total # good solutions after evaluation: ' + oneWaySolutions.length);

        callback(null, oneWaySolutions);
    });
}

我的日志控制台输出：

RailManager@findSolutionsOneWay, listResponseJson size 3
RailManager@findSolutionsOneWay,  # # # # # # processing response # : 0
RailManager@evaluateOneWaySolutions, no results to evaluate!
RailManager@findSolutionsOneWay,  # # # # # # processing response # : 1
RailManager@evaluateOneWaySolutions, isOutbound true
RailManager@evaluateOneWaySolutions, solutionList.length 6
RailManager@findSolutionsOneWay,  # # # # # # processing response # : 2
RailManager@evaluateOneWaySolutions, no results to evaluate!
RailManager@findSolutionsOneWay, total # good solutions after evaluation: 6
SearchTravelSolution.js: Cannot read property 'map' of undefined
TypeError: Cannot read property 'map' of undefined
    at _map (D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\node_modules\async\lib\async.js:54:16)
    at _asyncMap (D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\node_modules\async\lib\async.js:237:15)
    at Object.map (D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\node_modules\async\lib\async.js:219:23)
    at findSolutionsOneWay (D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\backgroundProcesses\searchTravelSolutions\RailManager.js:240:11)
    at D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\backgroundProcesses\searchTravelSolutions\RailManager.js:75:13
    at fn (D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\node_modules\async\lib\async.js:641:34)
    at Object._onImmediate (D:\Userfiles\oozen\Workspace\sas_1.0_server\sas_1.0\node_modules\async\lib\async.js:557:34)
    at processImmediate [as _immediateCallback] (timers.js:345:15)

我错过了什么？

编辑：调用findSolutionsOneWay

的函数

var findSolutions = function(tw){

    async.waterfall([
        function(callback) {

            // FIND ORIGIN STATIONS
            retrieveOriginRailStationCodes(tw, callback);

        }, function(vectorOriginStations, callback) {

            // FIND DESTINATION STATIONS
            retrieveDestinationRailStationCodes(tw, function(err, vectorDestinationStations){
                callback(err, vectorOriginStations, vectorDestinationStations);
            });

        }, function(vectorOriginStations, vectorDestinationStations, callback){

            buildRailURLs(tw, vectorOriginStations, vectorDestinationStations, callback);

        }, function(urls, callback){

             // FIND OUTBOUND SOLUTIONS
            findSolutionsOneWay(tw, urls.OutboundURLs, true, function(err, outboundSolutions){
                 callback(err, urls, outboundSolutions);
             });

        }, function( urls, outboundSolutions, callback){
            if(outboundSolutions.length == 0) {return next('no solutions found');}

            // FIND INBOUND SOLUTIONS
            findSolutionsOneWay(tw, urls.vectorInboundURLs, false, function(err, inboundSolutions){
                callback(err, outboundSolutions, inboundSolutions);
             });
        }
    ], function(err, outboundSolutions, inboundSolutions, tw) {

        console.log(TAG + '@findSolutions, # of outboundSolutions: ' + outboundSolutions.length);
        console.log(TAG + '@findSolutions, # of inboundSolutions : ' + inboundSolutions.length);

        var hasHotel = JsonInfo.getHasHotel(tw);

        if(hasHotel){
            retrieveHotelSolutions(outboundSolutions, inboundSolutions, tw); //TODO: the rest is without async.
        }
        else{
            console.log(' Error occurred! canT search for trains without hotel!')
        }
    });
}