实现viewmodels后jetpack组成应用程序，当我运行该应用程序时，它显示一个错误：-

试图对空对象引用java.lang调用接口方法“boolean java.util.Set.contains（java.lang.Object）”。尝试调用接口方法“boolean java.util.Set.contains（java.lang.Object）”，该方法位于com.example.android.ui.游戏视图模型中的空对象引用上。pickRandomWordAndShuffle（游戏视图模型.kt：21）位于com. example. android. ui.游戏视图模型中。（游戏视图模型.kt：10）

下面是我代码：-

import androidx.lifecycle.ViewModel
import com.example.android.unscramble.data.allWords
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow

class GameViewModel : ViewModel() {
    private val _uiState =
        MutableStateFlow(GameUiState(currentScrambledWord = pickRandomWordAndShuffle()))
    val uiState: StateFlow<GameUiState> = _uiState.asStateFlow()

    private var _count = 0
    val count: Int
        get() = _count

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

    private fun shuffleCurrentWord(word: String): String {
        val tempWord = word.toCharArray()
        // Scramble the word
        tempWord.shuffle()
        while (String(tempWord) == word) {
            tempWord.shuffle()
        }
        return String(tempWord)
    }

    private fun pickRandomWordAndShuffle(): String {
        // Continue picking up a new random word until you get one that hasn't been used before
        currentWord = allWords.random()
        if (usedWords.contains(currentWord)) {
            return pickRandomWordAndShuffle()
        } else {
            usedWords.add(currentWord)
            return shuffleCurrentWord(currentWord)
        }
    }

    private fun resetGame() {
        usedWords.clear()
        _uiState.value = GameUiState(currentScrambledWord = pickRandomWordAndShuffle())
    }
    init {
        resetGame()
    }
}

它没有显示任何编译时错误。我不知道该怎么办。