Commits
François Saint-Jacques authored and Antoine Pitrou committed ceaed810e6e
ARROW-4787: [C++] Add support for Null in MemoTable and related kernels Author: François Saint-Jacques <fsaintjacques@gmail.com> Closes #4480 from fsaintjacques/ARROW-4787-hash-nulls and squashes the following commits: 3e2b30eca <François Saint-Jacques> Fix python unique test 9cb73b8fe <François Saint-Jacques> Add option to skip memotable in HashKernel 4f7aa5331 <François Saint-Jacques> Fix MVCC again 16aa21181 <François Saint-Jacques> Fix MVCC warnings 8736606f2 <François Saint-Jacques> Fix typo de1957681 <François Saint-Jacques> Add null supports to kernels 2322ead49 <François Saint-Jacques> Add GetNull and GetOrInsertNull to MemoTable b85b8f4f3 <François Saint-Jacques> Add kKeyNotFound to memo table