sub-key 'non_existent' is not set.
sub-key 1 is set: string(1) "o"
-------------------
sub-sub-key 'sub_sub' is not set.
sub-sub-key 0 is set: string(1) "o"
-------------------
sub-key 'non_existent' is empty.
sub-key 1 is not empty: string(1) "o"
-------------------
sub-sub-key 'sub_sub' is empty.
sub-sub-key 0 is not empty: string(1) "o"
DONE