<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def sparkline_size(self, sparkline_size):
 """Sets the sparkline_size of this ChartSettings. For the single stat view, a misleadingly named property. This determines whether the sparkline of the statistic is displayed in the chart BACKGROUND, BOTTOM, or NONE # noqa: E501 :param sparkline_size: The sparkline_size of this ChartSettings. # noqa: E501 :type: str """

        allowed_values = ["BACKGROUND", "BOTTOM", "NONE"]  # noqa: E501
        if sparkline_size not in allowed_values:
            raise ValueError(
                "Invalid value for `sparkline_size` ({0}), must be one of {1}"  # noqa: E501
                .format(sparkline_size, allowed_values)
            )

        self._sparkline_size = sparkline_size