Roborio to Arduino i2c Code Not Working

[icg]

We keep getting this error:
ERROR  1  Unhandled exception: java.lang.NullPointerException  frc.robot.subsystems.ArduinoSubsystem.write(ArduinoSubsystem.java:29)

In our command file, we have

protected void execute() {

        Robot.LED.write("1");

}

And our subsystem file has

	public void write(String input){//writes to the arduino 
			char[] CharArray = input.toCharArray();//creates a char array from the input string
			byte[] WriteData = new byte[CharArray.length];//creates a byte array from the char array
			for (int i = 0; i < CharArray.length; i++) {//writes each byte to the arduino
				WriteData[i] = (byte)CharArray[i];//adds the char elements to the byte array 
			}
			Wire.transaction(WriteData, WriteData.length, null, 0);//sends each byte to arduino
	}

Why is this creating this error? All we want is to send integer values to the arduino.

[SamCarlberg]

Without access to the full code files (and line numbers) it’s hard to help. But something on line 29 of the arduino subsystem is null. Based on what you’ve shared, I’d bet the input string is being passed as null. Can’t help much more than that without being able to see your full program

[icg]

How could it be being passed as null though if we call the write method with the parameter “1”???

[SamCarlberg]

I can’t help any further without being able to see your program

[icg]

This is our arduinosubsystem file as of now:

package frc.robot.subsystems;

import frc.robot.Robot;
import edu.wpi.first.wpilibj.I2C;
import frc.robot.OI;
import edu.wpi.first.wpilibj.I2C.Port;
import edu.wpi.first.wpilibj.smartdashboard.*;
import edu.wpi.first.wpilibj.command.Subsystem;
import frc.robot.commands.ArduinoCommand;

public class ArduinoSubsystem extends Subsystem {

	private static I2C Wire = new I2C(Port.kOnboard, 4);//uses the i2c port on the RoboRIO													//uses address 4, must match arduino
	private static final int MAX_BYTES = 32;

	//String status = "";

	public void write(String input){//writes to the arduino 
			char[] CharArray = input.toCharArray();//creates a char array from the input string
			byte[] WriteData = new byte[CharArray.length];//creates a byte array from the char array
			for (int i = 0; i < CharArray.length; i++) {//writes each byte to the arduino
				WriteData[i] = (byte)CharArray[i];//adds the char elements to the byte array 
			}
			Wire.transaction(WriteData, WriteData.length, null, 0);//sends each byte to arduino
	}

	public Arduino getArduino(){//reads the data from arduino and saves it
		String info[] = read().split("\\|");//everytime a "|" is used it splits the data,
		Arduino arduino = new Arduino();  //creates a new packet to hold the data 
		if(info[0].equals("none") || info[0].equals("")){//checks to make sure there is data 
			arduino.x = -1;//the x val will never be -1 so we can text later in code to make sure 
			arduino.y = -1;
			arduino.area = -1;
			if (info.length >= 2) {
				arduino.distance = Double.parseDouble(info[1]);
			}
		}else if(info.length >= 3){//if there is an x, y, and area value the length equals 3
			arduino.x = Double.parseDouble(info[0]);//set x
			arduino.y = Double.parseDouble(info[1]);//set y
			arduino.area = Double.parseDouble(info[2]);//set area
			arduino.distance = Double.parseDouble(info[3]);
		}
		return arduino;
	}

	public void getData() {
		Arduino receive = getArduino();
		//System.out.println(receive.distance);
		if (OI.leftJoystick.getRawButtonPressed(12)) {
			System.out.println("Pixy:" + receive.x + " | " + receive.y + " | " + receive.area);
			System.out.println("Distance: " + receive.distance);
		}
	}

	private String read(){//function to read the data from arduino
		byte[] data = new byte[MAX_BYTES];//create a byte array to hold the incoming data
		Wire.read(4, MAX_BYTES, data);//use address 4 on i2c and store it in data
		String output = new String(data);//create a string from the byte array
		int pt = output.indexOf((char)255);
		return (String) output.subSequence(0, pt < 0 ? 0 : pt);
	}

	public void initDefaultCommand() {
        setDefaultCommand(new ArduinoCommand());
	}
	
}

In arduinocommand, we have only the basic command files and the thing in the execute

[Joe_Ross]

From the documentation:

public boolean transaction​(byte[] dataToSend, int sendSize, byte[] dataReceived, int receiveSize)

Generic transaction.

This is a lower-level interface to the I2C hardware giving you more control over each transaction. 
If you intend to write multiple bytes in the same transaction and do not plan to receive anything 
back, use writeBulk() instead. Calling this with a receiveSize of 0 will result in an error.

You are both passing a null and a receiveSize of 0.