For non-deterministic expressions, they should be considered as not contained in the [[ExpressionSet]].
This is consistent with how we define `semanticEquals` between two expressions.
Otherwise, combining expressions will remove non-deterministic expressions which should be reserved.
Combine filters of
testRelation.where(Rand(0) > 0.1).where(Rand(0) > 0.1)
should result in
testRelation.where(Rand(0) > 0.1 && Rand(0) > 0.1)