Error while fitting data to the model: TypeError: 'NoneType' object is not callable

I am using this code for the generator:

train_generator = train_datagen.flow_from_directory("C:\\Users\\Rahul\\Desktop\\AI\\Audio\\Classifying music notes\\output\\train",
                                                batch_size = 20,
                                                class_mode = 'binary', 
                                                target_size = (864, 432))  

 


validation_generator =  test_datagen.flow_from_directory( "C:\\Users\\Rahul\\Desktop\\AI\\Audio\\Classifying music notes\\output\\val",
                                                      batch_size  = 20,
                                                      class_mode  = 'binary', 
                                                      target_size = (864, 432))

I am getting this error when I run the below code: TypeError: 'NoneType' object is not callable

history = model.fit_generator(
        train_generator,
        validation_data = validation_generator,
        steps_per_epoch = 100,
        epochs = 100,
        validation_steps = 50,
        verbose = 2,
        callbacks=[callbacks])