chartjs: How to remove specific label

I have a Bar Chart with these data and options:

var data = {
    labels: periodnames,
    datasets: [          
        {
            yAxisID: "bar-stacked",
            data: rcash,
            backgroundColor: "#FFCE56",                  
            label:""
        },
    {
        yAxisID:"bar-stacked",
        data: pcash,
        backgroundColor: "#FFCE56",
        label: "cash"           

    }       

    ]

};

var options = {        
    animation: {
        animateScale: true
    },        
    scales: {
        xAxes: [{
        stacked: true,
    }],        
        yAxes: [ 
            {
                display:false,
                id: "line-axis",                  

            },
            {
            id: "bar-stacked",
            stacked: true,                

        }            
        ]
    }
}

finactivityGraphChart = new Chart(ctx, {
    type: 'bar',
    data: data,
    options: options
});

The result chart is this:

My problem is that I don't want to show the first dataset's label. If I don't define it, it shows the yellow box with the value "undefine" next to it. I suppose that I must modify the Chart.js file. Any suggestions?