NullPointerException at drivecode

[r0306]

When we run our drive code, it throws the following error:

[cRIO] java.lang.NullPointerException
[cRIO]     at edu.wpi.first.wpilibj.RobotDrive.arcadeDrive(RobotDrive.java:342)
[cRIO]     at edu.wpi.first.wpilibj.RobotDrive.arcadeDrive(RobotDrive.java:354)
[cRIO]     at Robot2013.RobotMain.teleopPeriodic(RobotMain.java:90)
[cRIO]     at edu.wpi.first.wpilibj.IterativeRobot.startCompetition(IterativeRobot.java:165)
[cRIO]     at edu.wpi.first.wpilibj.RobotBase.startApp(RobotBase.java:169)
[cRIO]     in virtual method #10 of javax.microedition.midlet.MIDlet(bci=17)
[cRIO]     at javax.microedition.midlet.MIDletTunnelImpl.callStartApp(64)
[cRIO]     at com.sun.squawk.imp.MIDletMainWrapper.main(110)
[cRIO]     in virtual method #95 of com.sun.squawk.Klass(bci=25)
[cRIO]     at com.sun.squawk.Isolate.run(1506)
[cRIO]     at java.lang.Thread.run(231)
[cRIO]     in virtual method #47 of com.sun.squawk.VMThread(bci=42)
[cRIO]     in static method #3 of com.sun.squawk.VM(bci=6)

public class RobotMain extends IterativeRobot
{

    public static RobotDrive driveTrain;
    public static Joystick leftStick; 
    
    public void robotInit()
    {

        driveTrain = new RobotDrive(4, 3, 1, 2);

        driveTrain.setSafetyEnabled(false);

    }


    public void autonomousPeriodic()
    {
        
    }

    public void teleopPeriodic()
    {

        driveTrain.arcadeDrive(leftStick); //line 90

    }

    public void testPeriodic() {

    }
}

The motors aren't running at all and I don't get what could've gone wrong here as the code seems fine.