Why this sequential model is not starting? I am using following code: 

input_shape = (75, 75, 3)
x = Input(input_shape)
model = BatchNormalization(axis = 3)(x)


Above code works all right. However, following code does not work: 

from keras.models import Sequential
input_shape = (64,64,3)
model = Sequential()
model = model.add(InputLayer(input_shape=input_shape))
model = model.add(BatchNormalization(axis = 3))


But at last line, I get error: 

AttributeError: 'NoneType' object has no attribute 'add'


If I change to: 

model = model.add(Input(input_shape))


I get following error: 

TypeError: The added layer must be an instance of class Layer. 
Found: Tensor("input_1:0", shape=(?, 64, 64, 3), dtype=float32)


Where is the problem and how can it be solved?

(PS: If you find this question to be interesting/important, please upvote it.)
from keras.models import Sequential
from keras.layers import InputLayer

model = Sequential()
model.add(InputLayer(input_shape))
model.add(BatchNormalization(axis = 3))


This should work. The first error was because the model was getting reassigned. The second error was because 'Input' is a function of 'layers' class but not a class, 'InputLayer' is a class.