What I contributed

I updated FTPClient to handle FTP servers that return 0,0,0,0 in a passive-mode response. In that case, the client now falls back to the server address from the control connection instead of trying to connect to an unusable address.

Why it mattered

The fix prevents passive FTP connection failures with servers and network configurations that replace the advertised data-channel address with zeroes.

The change was later integrated upstream through Apache Commons Net PR #28 under issue NET-649.