问python代码报错KeyError：-1，请问如何解决？

wavs = glob.glob('A2_103.wav')

print(wavs)

with open('dictionary.pkl', 'rb') as fr:

[char2id, id2char, mfcc_mean, mfcc_std] = pickle.load(fr)

mfcc_dim = 13

model = load_model('asr.h5')

index = np.random.randint(len(wavs))

print(wavs[index])

audio, sr = librosa.load(wavs[index])

energy = librosa.feature.rmse(audio)

frames = np.nonzero(energy >= np.max(energy) / 5)

indices = librosa.core.frames_to_samples(frames)[1]

audio = audio[indices[0]:indices[-1]] if indices.size else audio[0:0]

X_data = mfcc(audio, sr, numcep=mfcc_dim, nfft=551)

X_data = (X_data - mfcc_mean) / (mfcc_std + 1e-14)

print(X_data.shape)

pred = model.predict(np.expand_dims(X_data, axis=0))

pred_ids = K.eval(K.ctc_decode(pred, [X_data.shape[0]], greedy=False, beam_width=10, top_paths=1)[0][0])

pred_ids = pred_ids.flatten().tolist()

print(''.join([id2char[i] for i in pred_ids]))

运行这段代码之后报错

print(''.join([id2char[i] for i in pred_ids]))

KeyError: -1

请问该怎么解决呢