FTPSClient defaults to providing the TrustManager provided by FTPSTrustManager.

It should be possible to use setTrustManager(null) to obtain the default JVM trust manager, however this fails with

java.security.cert.CertificateException: No X509TrustManager implementation available

because SSLContext.init(KeyManager[] km, TrustManager[] tm, SecureRandom random) expects null parameters, but does not allow for null entries in the TrustManager array.

The init call needs to be changed so null is passed instead of an array with a null entry.