/* If there is no filter command set up, call the internal function that does
the actual work, passing it the incoming fd, and return its result. */
-if (transport_filter_argv == NULL)
+if ( !transport_filter_argv
+ || !*transport_filter_argv
+ || !**transport_filter_argv
+ )
return internal_transport_write_message(addr, fd, options, size_limit,
add_headers, remove_headers, check_string, escape_string,
rewrite_rules, rewrite_existflags);