TST: Fix tests for equality operator method
BUG: Add check for same type
TST: Fix tests for test_ne
BUG/TST: Add check for type of table
BUG: Type was not being defaulted to None

If the value was an empty string the value was not being defaulted to
None, hence causing some problems.
TST: Fix tests for test_getitem
TST: Fix test_nnz tests