If ma_values is NULL, the table is "combined": keys and values are stored in ma_keys.
If ma_values is not NULL, the table is split: keys are stored in ma_keys and values are stored in ma_values
See Implementation
If ma_values is NULL, the table is "combined": keys and values are stored in ma_keys.
If ma_values is not NULL, the table is split: keys are stored in ma_keys and values are stored in ma_values