Returns a new map containing the current map plus the given key:value.
However, if the given key already exists in the set,
it will remove the old one and add the new one.
The entries of the given imap will be added to the original map.
Note: imap entries that already exist in the original map will overwrite
those of the original map.
The entries will be added to the original map.
Note: entries that already exist in the original map will overwrite
those of the original map, in place (keeping order).
The map entries will be added to the original map.
Note: map entries that already exist in the original map will overwrite
those of the original map, in place (keeping order).