DeepLearning Chainer predictの時に __call__() missing 1 required positional argument: 'x'

Chainerで学習させたモデルを読み込んでpredictしようとしているのですがタイトルのようなエラーが出てしまいます。
引数の数もあっているはずなので原因がわかりません。
どこがまずいのでしょうか？

python
1def predict(model, dataset):
2    img, label = dataset
3    y = 0
4    with chainer.using_config('train', False), chainer.using_config('enable_backprop', False):
5        y = model(img) #ここでエラー
6    print("Predict : ", y.argmax(axis=1)[0], "Answer : ", label)
7    if y.argmax(axis=1)[0] == label:
8        return 1
9    else:
10        return 0
11
12def main():
13    model = L.Classifier(NIN(args.classes))
14    serializers.load_npz(args.model, model)
15    p_imgs = ######## #chainer用に画像を読み込む処理(tuple_dataset)
16    correct, total = 0, 0
17    for dataset in p_imgs:
18        correct += predict(model, dataset)
19        total += 1
20    print("Accuracy : ", correct*1.0/total)
21    return

python
1class NIN(chainer.Chain):
2
3    def __init__(self, n_out):
4        super(NIN, self).__init__()
5        conv_init = I.HeNormal()  # MSRA scaling
6        self.n_out = n_out
7        with self.init_scope():
8            self.mlpconv1 = L.MLPConvolution2D(
9                None, (96, 96, 96), 11, stride=4, conv_init=conv_init)
10            self.mlpconv2 = L.MLPConvolution2D(
11                None, (256, 256, 256), 5, pad=2, conv_init=conv_init)
12            self.mlpconv3 = L.MLPConvolution2D(
13                None, (384, 384, 384), 3, pad=1, conv_init=conv_init)
14            self.mlpconv4 = L.MLPConvolution2D(
15                None, (1024, 1024, self.n_out), 3, pad=1, conv_init=conv_init)
16
17    def __call__(self, x):
18        h = F.max_pooling_2d(F.relu(self.mlpconv1(x)), 3, stride=2)
19        h = F.max_pooling_2d(F.relu(self.mlpconv2(h)), 3, stride=2)
20        h = F.max_pooling_2d(F.relu(self.mlpconv3(h)), 3, stride=2)
21        h = self.mlpconv4(F.dropout(h))
22        h = F.reshape(F.average_pooling_2d(h, 6), (len(x), self.n_out))
23        return h

error
1Traceback (most recent call last):
2  File "predict.py", line 98, in <module>
3    main()
4  File "predict.py", line 91, in main
5    print(model(dataset[0]))
6  File "/Users/username/.pyenv/versions/3.7.0/lib/python3.7/site-packages/chainer/links/model/classifier.py", line 134, in __call__
7    self.y = self.predictor(*args, **kwargs)
8TypeError: __call__() missing 1 required positional argument: 'x'