Draws a horizontal stacked bar chart with different colors
        for each count of nan values per label.

def draw_stacked_bar(self, nan_col_counts):
        """Draws a horizontal stacked bar chart with different colors
        for each count of nan values per label.
        """
        for index, nan_values in enumerate(nan_col_counts):
            label, nan_col_counts = nan_values

            if index == 0:
                # first draw should be at zero
                bottom_chart = np.zeros(nan_col_counts.shape)

            # if features passed in then, label as such
            if self.classes_ is not None:
                label = self.classes_[index]

            color = self.colors[index]

            self.ax.barh(self.ind - self.width / 2, nan_col_counts, self.width,
                        color=color, label=label, left=bottom_chart)

            # keep track of counts to build on stacked
            bottom_chart = nan_col_counts