Merged requested to merge th/ghash-steal-extended-doc into main
GHashTable is optimized for using g_hash_table_add(), where the key and the value are identical.
When using g_hash_table_steal_extended() on such a dictionary, and requesting both a key and a value, then the stolen value will be NULL.
That would be easy to fix, but it also would be an API break. Instead, document this behavior.