JUnit5在预期另一种异常时获取NullPointerException

我试着测试一个简单的类,我在测试一个例子,如果我把一个字符串放进一个方法中,如果这个方法不是某个列表(侧臂)的一部分,它应该返回一个illegalArguementException。在本例中:“非沙漠之鹰”不在数组列表中。但为什么测试失败并返回它预期的IllegalArguementException,但实际上是nullPointerException?

测试课程:

package RandomClassGenerator;

import static org.junit.jupiter.api.Assertions.assertThrows;

import org.junit.jupiter.api.Test;

public class SidearmTest {
    
    private Sidearm sideArm;
    private String sidearm = "NOT Desert Eagle";

    @Test
    public void testSidearm() {
        assertThrows(IllegalArgumentException.class, () -> {
            sideArm.sidearmAttachment(sidearm);
        });
        
    }

被测试的班级:

import java.util.Arrays;
import java.util.List;

public class Sidearm implements IGiveRandom{
    
    // This class gives the player a sidearm with/without an attachment, as long as Overkill is not a given perk

    private String sidearm;
    private String sidearmAttachment;

    private List<String> sidearms = Arrays.asList("M9","USP.45","M1911.45","Desert Eagle");
    private List<String> sidearmAttachments = Arrays.asList("None","Silencer");

    // Constructor:
    public Sidearm() {
        sidearm = sidearm();
        sidearmAttachment = sidearmAttachment(sidearm);
    }
    // Gives a random sidearm from the sidearms array list
    public String sidearm() {
        int randomFromList = rand.nextInt(sidearms.size());
        sidearm = sidearms.get(randomFromList);
        return sidearm;
    }
    // Randomely, either gives or not, an attachment for the sidearm:
    public String sidearmAttachment(String weapon) {
        // The Desert Eagle has no attachments
        if (!(sidearms.contains(weapon))) throw new IllegalStateException("Sidearm not found");
        if (sidearm.equals("Desert Eagle")) {
            sidearmAttachment = "None";
        } else {
            // The rest of the sidearms can either have a silencer or no attachment
            int randomFromList = rand.nextInt(sidearmAttachments.size());
            sidearmAttachment = sidearmAttachments.get(randomFromList);
        }
        return sidearmAttachment;
    }