tensorflow - 'NoneType' object is not subscriptable ...
https://stackoverflow.com/questions/5739137706.08.2019 · Its a bug in tf.keras, they deprecated the validation_data parameter and no longer set the validation_data of the callback, its always set to None.. Your option is not to use tf.keras and just use the official keras package, I tested your code and it works in Keras 2.2.4. Alternatively you could also just pass your validation data to the __init__ of your callback and set it there.