Doughnut/Pie generateLabels assumes backgroundColor is always set on dataset

[tannerlinsley]

In the doughnut chart defaults, the generateLabels function assumes that data.datasets[0].backgroundColor is always set, resulting in the classic Cannot read property '0' of undefined error

labels: {
    generateLabels: function(data) {
        if (data.labels.length && data.datasets.length) {
            return data.labels.map(function(label, i) {
                return {
                    text: label,
                    fillStyle: data.datasets[0].backgroundColor[i],
                    hidden: isNaN(data.datasets[0].data[i]),

                    // Extra data used for toggling the correct item
                    index: i
                };
            });
        } else {
            return [];
        }
    }
},

[etimberg]

We could look at the objects and see what backgroundColor is set and use that.

The legend isn't great here since it assumes the color is the same for all datasets 😞