Unit test with Moq returns Object reference not set to an instance of an object. when calling method Base.GetAsync()

I am trying to do a unit test with Moq for this method:

public class XsService : EntityResourceService<XModel, string>, IXResourceService<XModel, string>
{
private readonly IXsEntityRepository<XModel, string> XEntityRepository;
Public XsService(
iCorrelationContextAccessor correlationContextAccessor,
IJsonApiContext jsonApiContext,
IXsEntityRepository<XModel, string> XEntityRepository) : 
base(jsonApiContext,   XEntityRepository)
{
this.XEntityRepository = XEntityRepository;
}

public async Task<IEnumerable<XModel>> GetXsAsync(UModel uModel)
{
await XEntityRepository.GetAllAsync(uModel.UserId);
return await base.GetAsync(); 
}
}

This is my unit test:

var uModels = new List<UModel>()
{
new UModel { Id = "12341", Name="group_name1" },
new UModel { Id = "12342", Name="group_name1" }
};

[Fact]
public async Task GetUAsync_Ok()
{
//Mocking base class
var baseClassMock = new Mock<XsService>(correlationContextAccessor, 
JsonApiContextMock.Object, userGroupsEntityRepositoryMock.Object) { CallBase = true };
baseClassMock.Setup(x => x.GetAsync()).Returns(Task.FromResult(uModels));

// Act            
var res = baseClassMock.Object.GetXsAsync(parameter);

// Assert
Assert.Equal("", "");
}

the Error is thrown when reaching the line:

return await base.GetAsync();

Error:

System.NullReferenceException HResult=0x80004003 Message=Object reference not set to an instance of an object. Source=JsonApiDotNetCore StackTrace: at JsonApiDotNetCore.Services.EntityResourceService`3.GetAsyncd__8.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

This exception was originally thrown at this call stack: JsonApiDotNetCore.Services.EntityResourceServiceTResource, TEntity, TId.GetAsync() System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

Maybe I need to moq EntityResourceService, like this:

var eRS = new Mock<EntityResourceService<UModel, string>>(jsonApiContextMock.Object, 
userGroupsEntityRepositoryMock.Object, null);
eRS.Setup(x => x.GetAsync()).Returns(Task.FromResult(userGroupModels));
      
var x = eRS.Object.GetAsync();

But, how can I inject that into the moq when creating the class instance?

This is the GetAsync method code

// MyModelService.cs
public class MyModelService : IResourceService<MyModel>
{
private readonly IMyModelDao _dao;

public MyModelService(IMyModelDao dao)
{ 
    _dao = dao;
} 

public Task<IEnumerable<MyModel>> GetAsync()
{
    return await _dao.GetModelAsync();
}

}