Function fz_hash_insert 

pub unsafe extern "C" fn fz_hash_insert(
    ctx: *mut fz_context,
    table: *mut fz_hash_table,
    key: *const c_void,
    val: *mut c_void,
) -> *mut c_void

Insert a new key/value pair into the hash table.

If an existing entry with the same key is found, no change is
made to the hash table, and a pointer to the existing value is
returned.

If no existing entry with the same key is found, ownership of
val passes in, key is copied, and NULL is returned.