code: def histogram_voltage(self, timestep=None, title=True, **kwargs):
          
          data = self.network.results.v_res()
          if title is True:
              if timestep is not None:
                  title = "Voltage histogram for time step {}".format(timestep)
              else:
                  title = "Voltage histogram \nfor time steps {} to {}".format(
                      data.index[0], data.index[-1])
          elif title is False:
              title = None
          plots.histogram(data=data, title=title, timeindex=timestep, **kwargs)
docs: Plots histogram of voltages.
  
          For more information see :func:`edisgo.tools.plots.histogram`.
  
          Parameters
          ----------
          timestep : :pandas:`pandas.Timestamp<timestamp>` or None, optional
              Specifies time step histogram is plotted for. If timestep is None
              all time steps voltages are calculated for are used. Default: None.
          title : :obj:`str` or :obj:`bool`, optional
              Title for plot. If True title is auto generated. If False plot has
              no title. If :obj:`str`, the provided title is used. Default: True.