Can't load Sequential with custom layers

[t-ae]

Now Sequeltial.from_config doesn't have cutsom_objects argument.
Sequential with custom layers can create config, but can't restore from it.
Is it a specification?

And if I save/load such model, Sequential.from_config is called internally here. custom_objects is ignored and raises ValueError: Unknown layer.
I think it should check custom_objects is None if from_config doesn't have custom_objects argument.

Sample code

#!/usr/bin/env python

import os
from keras.models import Model, Sequential, load_model
from keras.layers import Input, InputLayer
from keras.engine.topology import Layer

class MyLayer(Layer):
    def __init__(self, **kwargs):
        super(MyLayer, self).__init__(**kwargs)

    def call(self, inputs):
        return inputs + 1

    def compute_output_shape(self, input_shape):
        return input_shape

    def get_config(self):
        return super(MyLayer, self).get_config()

modelB = Sequential([
    InputLayer([10]),
    MyLayer()
])
modelB.save("model.h5")
try:
    load_model("model.h5", custom_objects={"MyLayer": MyLayer})  # this fails
    print("Succeeded to load modelB.")
except:
    print("Failed to load modelB.")
os.remove("model.h5")

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[t-ae]

Handed over to #5995.
@ushakov
Thank you!