Applies necessary type transformation to the data before
        it is set on a ColumnDataSource.

def _postprocess_data(self, data):
        """
        Applies necessary type transformation to the data before
        it is set on a ColumnDataSource.
        """
        new_data = {}
        for k, values in data.items():
            values = decode_bytes(values) # Bytes need decoding to strings

            # Certain datetime types need to be converted
            if len(values) and isinstance(values[0], cftime_types):
                if any(v.calendar not in _STANDARD_CALENDARS for v in values):
                    self.param.warning(
                        'Converting cftime.datetime from a non-standard '
                        'calendar (%s) to a standard calendar for plotting. '
                        'This may lead to subtle errors in formatting '
                        'dates, for accurate tick formatting switch to '
                        'the matplotlib backend.' % values[0].calendar)
                values = cftime_to_timestamp(values, 'ms')
            new_data[k] = values
        return new_data