Heatmap to color cells even when all the values are the same

[chutzimir]

Currently when the table only plots one possible value (e.g., table of
NULL and 1), the cells with a value have no color. I thought this is
counterintuitive, so I tried a custom heatmap using the weather example.
Indeed, using Plotly as below I can get the same heatmap as now, but
when my table only has a single possible value I can still tell the
cells with values from those with no value because they are white.

    rendererOptions: {
        heatmap: {
            colorScaleGenerator: function(values) {
                var min, max;
                min = Math.min.apply(Math, values);
                max = Math.max.apply(Math, values);
                return Plotly.d3.scale.linear()
                    .domain([min, max])
                    .range(["white", "red"])
                ;
            }
        }
    },