JUnit NPE issue in Build

@Model(adaptables = SlingHttpServletRequest.class,
        adapters = {MultifieldCollectionModel.class},
        defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
public class MultifieldCollectionModelImpl implements MultifieldCollectionModel {

    private final String resourcePath;

    private final String multifieldName;

    private final @NonNull Resource resource;

    private final @NonNull List<Resource> multiCollection;

    @Inject
    public MultifieldCollectionModelImpl(@RequestAttribute(name = "resourcePath") String resourcePath,
                                         @RequestAttribute(name = "multifieldName") String multifieldName,
                                         @Self @Via("resource") @NonNull Resource resource) {
        this.resourcePath = resourcePath;
        this.multifieldName = multifieldName;
        this.resource = resource;
        multiCollection = new ArrayList<>();
    }

    @PostConstruct
    public void init() {
        if (resourcePath != null && multifieldName != null) {
            String multifieldResourcePath = String.join("/", resourcePath, multifieldName);
            ResourceResolver resolver = resource.getResourceResolver();
            Resource multifieldResource = resolver.getResource(multifieldResourcePath);
            if (multifieldResource != null) {
                multifieldResource.listChildren().forEachRemaining(multiCollection::add);
            }
        }
    }

    @Override
    public List<Resource> getMultifieldList() {
        return Collections.unmodifiableList(multiCollection);
    }

    @Override
    public int getMultifieldListSize() {
        return multiCollection.size();
    }
}

@ExtendWith({AemContextExtension.class, MockitoExtension.class})
class MultifieldCollectionModelImplTest {
    private static final String CONTENT = "content";
    private static final String CQ_PAGE = "cq:page";
    private static final String PAGE_TITLE = "Project Page";
    private static final String HYPERLINK = "hyperlink";
    private static final String MULTIFIELD_NAME = "multifieldName";
    private static final String RESOURCE_PATH = "resourcePath";
    private static final String TITLE = "title";
    private static final String URL = "url";

    private MultifieldCollectionModel model;
    @InjectMocks
    private MultifieldCollectionModelImpl model1;
    private final AemContext context = new AemContext();

    @BeforeEach
    void setUp() throws WCMException {
        context.addModelsForClasses(MultifieldCollectionModel.class);
        context.pageManager().create("/", CONTENT, CQ_PAGE, CONTENT);
        context.pageManager().create("/content", "brandA", CQ_PAGE, PAGE_TITLE);
        Page page = context.pageManager().create("/content/brandA", "en", CQ_PAGE, PAGE_TITLE);
        context.currentPage(page);
    }

    @Test
    void shouldReturnEmptyListIfRequestAttributeMultifieldIsNull() throws IllegalAccessException {
        writeField(model1, "multifieldName", null, true);
        writeField(model1, "resourcePath", "resource", true);
        model1.init();
        model1.getMultifieldListSize();
        assertEquals(Collections.emptyList(), model1.getMultifieldList());
    }

    @Test
    void shouldReturnEmptyListIfRequestAttributeResourceIsNull() throws IllegalAccessException {
        writeField(model1, "multifieldName", null, true);
        writeField(model1, "resourcePath", null, true);
        model1.init();
        model1.getMultifieldListSize();
        assertEquals(Collections.emptyList(), model1.getMultifieldList());
    }

    @Test
    void shouldReturnEmptyListIfResourceIsNull() {
        context.request().setAttribute(RESOURCE_PATH, "/content/brandA/en/jcr:content");
        context.request().setAttribute(MULTIFIELD_NAME, HYPERLINK);
        model = context.request().adaptTo(MultifieldCollectionModel.class);
        assertTrue(model.getMultifieldList().isEmpty());
    }

    @Test
    void shouldReturnEmptyListIfResourceHasNotChildResources() {
        context.request().setAttribute(RESOURCE_PATH, "/content/brandA/en/jcr:content");
        context.request().setAttribute(MULTIFIELD_NAME, HYPERLINK);
        context.create().resource("/content/brandA/en/jcr:content/hyperlink");
        model = context.request().adaptTo(MultifieldCollectionModel.class);

        assertTrue(model.getMultifieldList().isEmpty());
    }

    @Test
    void shouldReturnMultifieldListIfResourceExist() {
        context.request().setAttribute(RESOURCE_PATH, "/content/brandA/en/jcr:content");
        context.request().setAttribute(MULTIFIELD_NAME, HYPERLINK);
        context.create().resource("/content/brandA/en/jcr:content/hyperlink");
        context.create()
            .resource("/content/brandA/en/jcr:content/hyperlink/item0", ImmutableMap.<String, Object>builder()
                .put(TITLE, "Products")
                .put(URL, "/content/products")
                .build());
        context.create()
            .resource("/content/brandA/en/jcr:content/hyperlink/item1", ImmutableMap.<String, Object>builder()
                .put(TITLE, "Campaigns")
                .put(URL, "/content/campaigns")
                .build());
        model = context.request().adaptTo(MultifieldCollectionModel.class);

        assertEquals("Products", model.getMultifieldList().get(0).getValueMap().get(TITLE, String.class));
        assertEquals("/content/products", model.getMultifieldList().get(0).getValueMap().get(URL,
            String.class));
        assertEquals("Campaigns", model.getMultifieldList().get(1).getValueMap().get(TITLE, String.class));
        assertEquals("/content/campaigns", model.getMultifieldList().get(1).getValueMap().get(URL,
            String.class));
    }

    @Test
    void shouldReturnMultifieldListSizeIfResourceExist() {
        context.request().setAttribute(RESOURCE_PATH, "/content/brandA/en/jcr:content");
        context.request().setAttribute(MULTIFIELD_NAME, HYPERLINK);
        context.create().resource("/content/brandA/en/jcr:content/hyperlink");
        context.create()
            .resource("/content/brandA/en/jcr:content/hyperlink/item0", ImmutableMap.<String, Object>builder()
                .put(TITLE, "Products")
                .put(URL, "/content/products")
                .build());
        context.create()
            .resource("/content/brandA/en/jcr:content/hyperlink/item1", ImmutableMap.<String, Object>builder()
                .put(TITLE, "Campaigns")
                .put(URL, "/content/campaigns")
                .build());
        model = context.request().adaptTo(MultifieldCollectionModel.class);

        assertEquals(2, model.getMultifieldListSize());
    }
}

@Model(adaptables = SlingHttpServletRequest.class,
        adapters = {MultifieldCollectionModel.class, ComponentExporter.class},
        defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
@Exporter(name = ExporterConstants.SLING_MODEL_EXPORTER_NAME, extensions = ExporterConstants.SLING_MODEL_EXTENSION)
public class MultifieldCollectionModelImpl implements MultifieldCollectionModel {