Particle storm control property not working properly

while using particle storm plugin of phaser the control property like

alpha: {value: 1, delta: 0.01,control :[ { x: 0, y: 0 }, { x: 0.3, y: 1 }, { x: 1, y: 0 }] },

throwing error “TypeError: Cannot read property ‘y’ of undefined” in getValue method when switching tab in same browser window. Not able to find the actual cause. Any help would be really appreciable.

What’s on that line in the source?

@samme below is method of particle storm plugin

getValue: function (obj, percent) {

    if (!obj.control || percent === undefined)
    {
        return obj.value;
    }

    var point = obj.control[0];

    //  Very start of the graph?
    if (point.x === percent)
    {
        return point.y;
    }

    var index = obj.control.length - 1;

    //  Very end of the graph?
    var last = obj.control[index];

    if (last.x === percent)
    {
        return last.y;
    }

    index = 0;

    while (point.x <= percent)
    {
        if (index >= obj.control.length - 1)
        {
            return point.y;
        }

        point = obj.control[++index];
    }

    var prev = obj.control[index - 1];

    //  Linear interpolation: f(x) = y0 + (y1 - y0) * (x - x0) / (x1 - x0)
    return obj.value * (prev.y + (percent - prev.x) * (point.y - prev.y) / (point.x - prev.x));

},

index value is not getting incremented because here percentage is coming in negative