address this problem observed with sources' upas/fs
and nasty apple client:

acid: stk()
cistrstr(sub=0x2e359,s=0x0)+0x3c /sys/src/libc/port/cistrstr.c:16
searchMsg(m=0x37ee0,s=0x2e308)+0x515 /sys/src/cmd/ip/imap4d/search.c:105
searchUCmd(uids=0x1,tg=0x2e258,cmd=0x2e298)+0x99 /sys/src/cmd/ip/imap4d/imap4d.c:1086
uidCmd(tg=0x2e258,cmd=0x2e278)+0xb8 /sys/src/cmd/ip/imap4d/imap4d.c:1326
imap4(preauth=0x0)+0x15f /sys/src/cmd/ip/imap4d/imap4d.c:332
main(argv=0xdfffef8c,argc=0x0)+0x19c /sys/src/cmd/ip/imap4d/imap4d.c:281
_main+0x31 /sys/src/libc/386/main9.s:16
acid: lstk()

- erik

Reference: /n/sources/patch/applied/imap4dsrch
Date: Thu Jun 19 00:16:39 CES 2008
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ip/imap4d/search.c	Thu Jun 19 00:16:00 2008
+++ /sys/src/cmd/ip/imap4d/search.c	Thu Jun 19 00:15:58 2008
@@ -102,7 +102,9 @@
 			ok = addrSearch(m->to, s->s);
 			break;
 		case SKSubject:
-			ok = cistrstr(m->info[ISubject], s->s) != nil;
+			ok = 0;
+			if(m->info[ISubject])
+				ok = cistrstr(m->info[ISubject], s->s) != nil;
 			break;
 
 		case SKBefore: