What steps will reproduce the problem?
1. Call ftp.Size("this_file_doesnt_exist")

What is the expected output?

An error message.

What do you see instead?

A panic in client.go:402

Please provide any additional information below.

Fixed with...

401:  response, err := ftp.SendAndRead(SIZE_FTP_CMD, filename)
402:  if err != nil {
403:     return
494:  }