Crash when set pin length only on xml layout

[van-tran]

I set PinLockView widget's pinlenght = 6. It'll crash when entering the 5th digits. It seems default PIN length is 4. Error log below

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setBackgroundResource(int)' on a null object reference at com.andrognito.pinlockview.IndicatorDots.fillDot(IndicatorDots.java:148) at com.andrognito.pinlockview.IndicatorDots.updateDot(IndicatorDots.java:107) at com.andrognito.pinlockview.PinLockView$1.onNumberClicked(PinLockView.java:46) at com.andrognito.pinlockview.PinLockAdapter$NumberViewHolder$1.onClick(PinLockAdapter.java:191)