### Question:
ProtocolNegotiators { public static ProtocolNegotiator serverTls(final SslContext sslContext) { Preconditions.checkNotNull(sslContext, "sslContext"); return new ProtocolNegotiator() { @Override public Handler newHandler(GrpcHttp2ConnectionHandler handler) { return new ServerTlsHandler(sslContext, handler); } @Override public void close() {} }; } private  ProtocolNegotiators(); static ProtocolNegotiator serverPlaintext(); static ProtocolNegotiator serverTls(final SslContext sslContext); static ProtocolNegotiator httpProxy(final SocketAddress proxyAddress,
      final @Nullable String proxyUsername, final @Nullable String proxyPassword,
      final ProtocolNegotiator negotiator); static ProtocolNegotiator tls(SslContext sslContext); static ProtocolNegotiator plaintextUpgrade(); static ProtocolNegotiator plaintext();  }### Answer:
@Test public void tlsHandler_failsOnNullEngine() throws Exception { thrown.expect(NullPointerException.class); thrown.expectMessage("ssl"); Object unused = ProtocolNegotiators.serverTls(null); }