in order to obtain the desired result, you can try the following solution:
1) Add two Selector Units inside the page containing the Hierarchical Index Units.
Each Selector Unit is related to the Entity specified on a Hierarchical Index Unit (e.g. the Entity of the Selector Unit 1 is the same as the Entity specified on the Hierarchical Index Unit 1 at Level 0, and so on).
2) Add two variables: the first one refers to the "Data Size" parameter of the Selector Unit 1, while the second one refers to the "Data Size" parameter of the Selector Unit 2.
3) Add a Condition Expression working on the previous variables ("var1" and "var2" are the name of the variables):
def expr = var1 != 0 || var2 != 0
4) Select the Grid Cell containing the units and in the Condition tab, set the "Cell Visibility Cond." property to the Condition Expression.
In this way, if both Hierarchical Index Units are empty, the Grid Cell will be hidden.