docs: def _plot_histogram(series, bins=10, figsize=(6, 4), facecolor='#337ab7'):
      """Plot an histogram from the data and return the AxesSubplot object.
  
      Parameters
      ----------
      series : Series
          The data to plot
      figsize : tuple
          The size of the figure (width, height) in inches, default (6,4)
      facecolor : str
          The color code.
  
      Returns
      -------
      matplotlib.AxesSubplot
          The plot.
      """
      if base.get_vartype(series) == base.TYPE_DATE:
          # TODO: These calls should be merged
          fig = plt.figure(figsize=figsize)
          plot = fig.add_subplot(111)
          plot.set_ylabel('Frequency')
          try:
              plot.hist(series.dropna().values, facecolor=facecolor, bins=bins)
          except TypeError: # matplotlib 1.4 can't plot dates so will show empty plot instead
              pass
      else:
          plot = series.plot(kind='hist', figsize=figsize,
                             facecolor=facecolor,
                             bins=bins)  # TODO when running on server, send this off to a different thread
      return plot