Per some comments from Lars Kellogg-Stedman <lars@larsshack.org>,

make xreadlink() return NULL on failure, and make sure everyone
uses the interface correctly.
 -Erik

miscutils/readlink.c

@@ -37,6 +37,8 @@ int readlink_main(int argc, char **argv)
 		show_usage();
 
 	buf = xreadlink(argv[1]);
+	if (!buf)
+		return EXIT_FAILURE;
 	puts(buf);
 #ifdef BB_FEATURE_CLEAN_UP
 	free(buf);