L2-normalization with Keras Backend? - tensorflow

Question

I'd like to normalize the inputs going into my neural network but, as I'm defining my model in this way:
df = pd.read_csv(r'C:\Users\Davide Mori\PycharmProjects\pythonProject\Dataset.csv')
print(df)
target_column = ['W_mag', 'W_phase']
predictors = list(set(list(df.columns)) - set(target_column))
X = df[predictors].values
Y = df[target_column].values
def get_model(n_inputs, n_outputs):
model = Sequential()
model.add(Dense(1000,input_dim= n_inputs, activation='relu'))
#model.add(Lambda(lambda x: K.l2_normalize(x, axis=1)))
model.add(Dense(1000, activation='linear', activity_regularizer=regularizers.l1(0.0001)))
model.add(Activation('relu'))
model.add(Dense(n_outputs, activation='linear'))
model.compile(optimizer="adam", loss="mean_squared_error", metrics=["mean_squared_error"])
model.summary()
return model
n_inputs, n_outputs = X.shape[1], Y.shape[1]
model = get_model(n_inputs, n_outputs)
# fit the model on all data
model.fit(X, Y, epochs=100, batch_size=1)
how do I apply the lambda layer to my inputs? Isn't wrong the commented line position? Because If I put the lambda layer there I'm normalizing what is already be "transformed" by the first hidden layer,right? How can I solve this problem?
This is the error I have when putting the lambda layer before everything else :
2020-10-12 15:08:46.036872: I
tensorflow/core/platform/cpu_feature_guard.cc:142] Your CPU supports
instructions that this TensorFlow binary was not compiled to use: AVX AVX2
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "C:\Program Files\JetBrains\PyCharm
2020.2.2\plugins\python\helpers\pydev\_pydev_bundle\pydev_umd.py", line 197,
in runfile
pydev_imports.execfile(filename, global_vars, local_vars) # execute the
script
File "C:\Program Files\JetBrains\PyCharm
2020.2.2\plugins\python\helpers\pydev\_pydev_imps\_pydev_execfile.py", line
18, in execfile
exec(compile(contents+"\n", file, 'exec'), glob, loc)
File "C:/Users/Davide Mori/PycharmProjects/pythonProject/prova_rete_sfs.py",
line 60, in <module>
model = get_model(n_inputs, n_outputs)
File "C:/Users/Davide Mori/PycharmProjects/pythonProject/prova_rete_sfs.py",
line 52, in get_model
model.summary()
File "C:\Users\Davide Mori\Anaconda3\envs\pythonProject\lib\site-
packages\tensorflow_core\python\keras\engine\network.py", line 1302, in
summary
raise ValueError('This model has not yet been built. '
ValueError: This model has not yet been built. Build the model first by
calling `build()` or calling `fit()` with some data, or specify an
`input_shape` argument in the first layer(s) for automatic build.