NotImplementedError in jupyter notboook helppp mee plzz !!!

when i run this code i hoave a probleme NOTIMPLEMENTEDERREUR
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history = model.fit_generator(generator=train_gen,
validation_data=validate_gen,
steps_per_epoch=len(train_gen),
validation_steps=len(validate_gen),
verbose=1,
epochs=1,
callbacks=callbacks,
workers=7, # recommend: number of cpu cores\n",
use_multiprocessing=True)
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Erreur
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NotImplementedError Traceback (most recent call last)
in
1 history = model.fit_generator(generator=train_gen,
2 validation_data=validate_gen,
----> 3 steps_per_epoch=len(train_gen),
4 validation_steps=len(validate_gen),
5 verbose=1,

C:\ProgramData\Anaconda3\envs\tensorflow\lib\site-packages\keras\utils\data_utils.py in __len__(self)
366 The number of batches in the Sequence.
367 """
--> 368 raise NotImplementedError
369
370 def on_epoch_end(self):

NotImplementedError:
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