In gnumeric we had in xlsx export:
----------------------------------------------------
	authors = g_hash_table_new (g_str_hash, g_str_equal);
	for (ptr = objects; ptr; ptr = ptr->next) {
		authorname = cell_comment_author_get (CELL_COMMENT (ptr->data));
		if (!g_hash_table_lookup_extended (authors, authorname, NULL, NULL))
			g_hash_table_insert (authors, (gpointer) authorname, GUINT_TO_POINTER (author++));
	}
----------------------------------------------------
If authorname happens to be NULL this crashed inside g_hash_table_lookup_extended although its documentation clearly indicates that NULL can be used as a lookup_key:

Program received signal SIGSEGV, Segmentation fault.
0x01018733 in g_str_hash (v=0x0) at gstring.c:142
142	  for (p = v; *p != '\0'; p++)

We have the backtrace:

+ Trace 226054