GetPostsAsync.cs

public async Task<List<Post>> GetPostsAsync(string userId = null, PaginationFilter paginationFilter = null)
{
    var queryable = _dataContext.Posts.AsQueryable();

    if (paginationFilter == null)
    {
        return await queryable.Include(x => x.Tags).ToListAsync();
    }
    
    if (!string.IsNullOrEmpty(userId))
    {
        queryable = queryable.Where(x => x.UserId == userId);
    }
    ...
}