Can reproduce with latest make from CVS.  ns is null at the penultimate line:

2175                 /* In case user set .DEFAULT_GOAL to a non-existent target
2176                    name let's just enter this name into the table and let
2177                    the standard logic sort it out. */
2178                 if (default_goal_file == 0)
2179                   {
2180                     struct nameseq *ns;
2181                     char *p = *default_goal_name;
2182
2183                     ns = multi_glob (
2184                       parse_file_seq (&p, '\0', sizeof (struct nameseq), 1),
2185                       sizeof (struct nameseq));
2186
2187                     /* .DEFAULT_GOAL should contain one target. */
2188                     if (ns->next != 0)
2189                       fatal (NILF, _(".DEFAULT_GOAL contains more than one target"));