// get the global properties and clear unique fields (not preserved anyways during the union)
GlobalProperties p1 = c1.getGlobalProperties();
GlobalProperties p2 = c2.getGlobalProperties();
p1.clearUniqueFieldCombinations();
p2.clearUniqueFieldCombinations();
// adjust the partitionings, if they exist but are not equal. this may happen when both channels have a
// partitioning that fulfills the requirements, but both are incompatible. For example may a property requirement
// be ANY_PARTITIONING on fields (0) and one channel is range partitioned on that field, the other is hash
// partitioned on that field.