Added Set "null" string test case
Merge branch 'oidset'
Added Oid construct check and test case
Merge branch 'oid'
Added Set construct check and test case
Merge branch 'set'
Added SortedSet construct check and test case
Merge branch 'sortedset'
Added OidSet construct check and test case
Merge branch 'oidset'
Modify new Oid() test case same to other classes
Merge branch 'oid'