Attempt to invoke virtual method 'com.jcraft.jsch.Channel com.jcraft.jsch.Session.openChannel(java.lang.String)' on a null object reference     at createErrorFromErrorData

Below code gives error

SSHClient.setup("root","202.70.73.34",22);
SSHClient.usePrivateKey(false);
SSHClient.setPassword("mypassword");
SSHClient.connect();

SSHClient.execute("uname -a").then(
  (result)=>{
    alert(result);
  },
  (error)=>{
    console.log(error);
  }
);