How to solve class cast exception with optional class when doing unit testing in Springboot app

I am using Java 8. when I am trying to return a list of type Items(user defined), it is throwing class cast exception. can you please tell me what I am doing wrong?

here's the code.

@ExtendWith(MockitoExtension.class)
public class ItemsMicroserviceApplicationServiceTests {
    @Mock
    ItemRepo itemrepo;
    @InjectMocks
    ItemsService itemsService=new ItemsService();
    List<Items> itemList;
    @Test
    void testaddItemsService() 
    {
        itemList=new ArrayList<>();
        itemList.add(new Items(1,"oneplus","good smartwatch",5999));
        itemList.add(new Items(2,"realme","decent buds",3999));
       
       ItemListDto itemListDto=new ItemListDto(itemList);
       
       Optional<List<Items>> optionalList=Optional.of(itemList);
       
       when(itemsService.addItemsService(itemListDto)).thenReturn(optionalList);

       assertTrue(true);
    }
}

I have used assertTrue just to avoid the error but still I am getting it.

This is the error I am getting.

java.lang.ClassCastException: class java.util.Optional cannot be cast to class com.example.items.model.Items (java.util.Optional is in module java.base of loader 'bootstrap'; com.example.items.model.Items is in unnamed module of loader 'app')
    at com.example.items.repository.ItemRepo$MockitoMock$frrDWmzA.save(Unknown Source)
    at com.example.items.repository.ItemRepo$MockitoMock$frrDWmzA.save(Unknown Source)
    at com.example.items.service.ItemsService.lambda$0(ItemsService.java:45)
    at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625)
    at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
    at com.example.items.service.ItemsService.addItemsService(ItemsService.java:45)
    at com.example.items.demo.service.ItemsMicroserviceApplicationServiceTests.testaddItemsService(ItemsMicroserviceApplicationServiceTests.java:56)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:214)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:210)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)