Why the nullpointer exception

Question

I have a login screen where when i put information into the username and password field and then press login it calls the method below sendLogin(), but when I do so I get a nullpointer exception on the first patient.setUsername. I do get the println of what was entered into the txt fields. The txtFldUsername is a jtxtfield, and I have put information into it, yet it doesn't seem to be accepting it.
here is the error lines i have
username = hello
password = world
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at mmsi.loginScreen.sendLogin(loginScreen.java:217)
at mmsi.loginScreen.btnLoginActionPerformed(loginScreen.java:165)
at mmsi.loginScreen.access$000(loginScreen.java:16)
at mmsi.loginScreen$1.actionPerformed(loginScreen.java:67)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
also, when i put no information in, the program hangs, and i get no output.
public void sendLogin(){
        if (txtFldUsername.getText().trim().equals("") || pswrdFldPassword.getText().trim().equals("")){
            JOptionPane.showMessageDialog(null,"Complete empty field(s)","Warning",JOptionPane.WARNING_MESSAGE);
        } else {
           System.out.println("username = " + txtFldUsername.getText());
           System.out.println("password = " + pswrdFldPassword.getText());
            patient.setUsername(txtFldUsername.getText().trim());
            patient.setPassword(pswrdFldPassword.getText().trim());
            patient.setAction("login");
            trans.sendPatient(objOut, patient);
    }

Answer 1

patient.setUsername(txtFldUsername.getText().trim());
sorry didn't note it very well in my description