My Android app crashed on click button?

Question

My app cashes when i click submit, it doesnt verify the fields as it should.
It works the way i want to but if i click on submit without entering anything it crashes.

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button addBtn = (Button) findViewById(R.id.addBtn);
        addBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText amoutGiven = (EditText) findViewById(R.id.amountG);
                EditText manyPeople = (EditText) findViewById(R.id.mPeople);
                EditText moenyGiven = (EditText) findViewById(R.id.moneyG);
                TextView changeTxt  = (TextView) findViewById(R.id.changeTxt);
                Button nxtBtn     = (Button) findViewById(R.id.nxtBtn);
                Button tryBtn     = (Button) findViewById(R.id.tryBtn);
                android.view.inputmethod.InputMethodManager imm = (android.view.inputmethod.InputMethodManager)getSystemService(INPUT_METHOD_SERVICE);
                imm.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 0);

                if (amoutGiven.getText().length()==0){
                    amoutGiven.setError("This field is required");
                }

                if (manyPeople.getText().length()==0){
                    manyPeople.setError("This field is required");
                }

                if (moenyGiven.getText().length()==0){
                    moenyGiven.setError("This field is required");
                }

                int num1 = Integer.parseInt(amoutGiven.getText().toString());
                int num2 = Integer.parseInt(manyPeople.getText().toString());
                int num3 = Integer.parseInt(moenyGiven.getText().toString());
                int total = num1 * num2;
                int change = num3 - total;

                changeTxt.setVisibility((changeTxt.getVisibility() == View.VISIBLE)
                        ? View.INVISIBLE : View.VISIBLE);

                if (change < 0 ){
                    changeTxt.setText("Your numbers dont add up");
                    tryBtn.setVisibility((tryBtn.getVisibility() == View.VISIBLE)
                            ? View.INVISIBLE : View.VISIBLE);
                    tryBtn.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            startActivity(new Intent(MainActivity.this, MainActivity.class));

                        }
                    });

                }else {

                    changeTxt.setText( "Give Back Change oF: R" + change +"" );
                    nxtBtn.setVisibility((nxtBtn.getVisibility() == View.VISIBLE)
                            ? View.INVISIBLE : View.VISIBLE);
                    nxtBtn.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            startActivity(new Intent(MainActivity.this, MainActivity.class));    
                        }
                    });    
                }    
            }
        });    
    }
}