When I passed the several attibutes as the attrs argument to 
util_ldap_cache_getuserdn and the first attribute value from a LDAP entry was 
null, all attribute values weren't cached.

I think that the following codes in util_ldap_cache.c are causes.
If node->vals[0] is null, all node->vals[i] aren't copied to cache.

void *util_ldap_search_node_copy(util_ald_cache_t *cache, void *c)
...
        /* copy vals */
        if (node->vals) {
            int k = 0;
            int i = 0;
            while (node->vals[k++]);
            if (!(newnode->vals = util_ald_alloc(cache, sizeof(char *) * 
(k+1)))) {
                util_ldap_search_node_free(cache, newnode);
                return NULL;
            }
            while (node->vals[i]) {
                if (!(newnode->vals[i] = util_ald_strdup(cache, node->vals
[i]))) {
                    util_ldap_search_node_free(cache, newnode);
                    return NULL;
                }
                i++;
            }
        }
...