def get_array(self, period):
        """
            Get the value of the variable for the given period.

            If the value is not known, return ``None``.
        """
        if self.variable.is_neutralized:
            return self.default_array()
        value = self._memory_storage.get(period)
        if value is not None:
            return value
        if self._disk_storage:
            return self._disk_storage.get(period)
Get the value of the variable for the given period.

            If the value is not known, return ``None``.