Why is this constraint missing from ParameterBinding (in part 1)

context ParameterBinding

  -- Matching data type

  inv ParameterBindingTypes ('The provided \'DataUse\' shall conform to the \'DataType\' of the referenced \'Parameter\'.' + self.toString()):

        self.dataUse.resolveDataType().conformsTo(self.parameter.dataType)

  -- Members in 'reduction' list of parameter

  inv ReductionMembers ('The \'Member\' referenced by the \'MemberReference\' at index i of a \'reduction\' shall be contained in or inherited by the \'StructuredDataType\' of the \'Member\' referenced by the \'MemberReference\' at index (i - 1) of that \'reduction\' or the \'StructuredDataType\' of the \'parameter\' if the \'MemberReference\' is the first element of the \'reduction\'.' + self.toString()):

        self.reduction->isEmpty()