Amazon QuickSight now fully support NULL in parameter use. Parameter, as a place holder for single value or multi-value variables, is a powerful and widely used entity in QuickSight. Previously, NULL is not supported as a valid value for parameter, which created some discrepancies when user data has NULL value in it. With the full enablement for NULL, all functionalities consuming parameters are now supporting NULL value. Enablement of NULL in parameter provides a comprehensive experience when parameter is used in various cases. For further details, visit here.
Source:: Amazon AWS