参数2：无法转换为Expression <system.func <t，bool =“”>＆gt;到“System.func <t，bool =”“>”

Question

我使用this代码作为参考实现MongoDBRepository，但它给了我一个错误。

这是我的示例代码。

   public static IMongoCollection<Book> Initialize()
        {
                MongoClientSettings settings = new MongoClientSettings();
                settings.Server = new MongoServerAddress(host, 10255);
                settings.UseSsl = true;
                settings.SslSettings = new SslSettings();
                settings.SslSettings.EnabledSslProtocols = SslProtocols.Tls12;
                MongoIdentity identity = new MongoInternalIdentity(dbName, userName);
                MongoIdentityEvidence evidence = new PasswordEvidence(password);
                settings.Credentials = new List<MongoCredential>()
            {
                new MongoCredential("SCRAM-SHA-1", identity, evidence)
            };
                MongoClient client = new MongoClient(settings);
                var database = client.GetDatabase(dbName);
                var bookCollection = database.GetCollection<Book>(collectionName);
                return bookCollection;
        }
  public Task<IEnumerable<Models.Book>> GetBooksAsync(Expression<Func<Models.Book, bool>> predicate)
        {
            if (predicate == null) { throw new ArgumentNullException("Predicate is Null"); }
            var client = Initialize();
            return client.AsQueryable().Where(predicate);
        }

它在最后一行代码中的谓词下显示红色下划线。错误消息显示：

Argument 2: cannot convert from 'System.Linq.Expressions.Expression<System.Func<BookProfile.Models.Book, bool>>' to 'System.Func<Book, bool>'

有人可以解释这个问题的原因是什么吗？