index error while trying to fit model keras

i'm trying to create an autoencoder with keras, here's my code:

from keras import models, layers
from numpy import array
import random

data = array(
    [array([[random.randint(0, 100) for i in range(50)]]) for i in range(500)]
).reshape((500, 50))
model = models.Sequential()
model.add(layers.Dense(input_dim=50, units=50, activation="sigmoid"))
model.add(layers.Dense(units=40, activation="sigmoid"))
model.add(layers.Dense(units=50, activation="sigmoid"))
model.compile(optimizer="adam", loss="mean_squared_error", metrics=["accuracy"])
model.fit(data, epochs=1)

and my error is :

Python\Python36\lib\site-packages\keras\engine\training_arrays.py", line 139, in fit_loop
    if issparse(ins[i]) and not K.is_sparse(feed[i]):
IndexError: list index out of range