the append function is not defined

[fizwit]

bpt.c line 337; append is used as a variable and a function. The define in bpt.h is a function header but the function is not defined.

    // If the append function is NULL assume overwrite
    if (append != NULL)
        append(domain,
               value_id,
               BPT_POINTERS(target_bpt_node)[*target_key_pos],
               handler);
    else
        BPT_POINTERS(target_bpt_node)[*target_key_pos] = value_id;