This patch was fed back to the upstream community:

http://code.google.com/p/libarchive/issues/detail?id=286

Given the response "I applied your patch to zip writer."

it should no longer be needed with the next release.

--- libarchive/libarchive/archive_write_set_format_zip.c.orig	Mon Mar 26 19:49:00 2012

+++ libarchive/libarchive/archive_write_set_format_zip.c	Tue Nov 27 17:31:42 2012

@@ -842,6 +842,8 @@

 	type = archive_entry_filetype(entry);

 	path = archive_entry_pathname(entry);

+	if (path == NULL)

+		return (0);

 	if ((type == AE_IFDIR) & (path[strlen(path) - 1] != '/')) {

 		return strlen(path) + 1;

 	} else {