Android Basics: Viewmodel and State in Compose :NullPointerException in the tutorial code

[bsudhanva]

 Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'void java.util.Set.clear()' on a null object reference
                                                                                                    	at com.example.unscramble.ui.GameViewModel.resetGame(GameViewModel.kt:41)
                                                                                                    	at com.example.unscramble.ui.GameViewModel.<init>(GameViewModel.kt:14)

The app crashes at start, and stack trace points at init method that calls resetGame() function .
Specifically at [Link to tutorial page
Got the error while i was at step 6 of Link to tutorial page

As a mitigation I had added if else for null checking, even then it produces this error
Null safety code

fun resetGame(){
if (usedWords != null)
	{usedWords.clear()
		_uiState.value = GameUiState(currentScrambledWord = pickRandomWordAndShuffle())
    }

		else _uiState.value = GameUiState(currentScrambledWord = pickRandomWordAndShuffle())
}

Log cat says-

 Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.Set.contains(java.lang.Object)' on a null object reference
                                                                                                    	at com.example.unscramble.ui.GameViewModel.pickRandomWordAndShuffle(GameViewModel.kt:52)
                                                                                                    	at com.example.unscramble.ui.GameViewModel.resetGame(GameViewModel.kt:43)
                                                                                                    	at com.example.unscramble.ui.GameViewModel.<init>(GameViewModel.kt:14)

And for sake of testing if i remove else block and use Unit, app launches without any error , but then there is no scrambled word displayed .

complete null safety code -

if (usedWords != null)
	{usedWords.clear()
		_uiState.value = GameUiState(currentScrambledWord = pickRandomWordAndShuffle())}

		else Unit

[thomasem]

Seems like this is related to whether the init block is before or after usedWords is created, which should be initialized with an empty set like

    private var usedWords: MutableSet<String> = mutableSetOf()

If the init block that calls resetGame() is included before this line, it will throw a NullPointerException