class_docstr: Generic merge layer for elementwise merge functions.
  
  Used to implement `Sum`, `Average`, etc.
code: def _merge_function(self, inputs):
      raise NotImplementedError
  
imports: from tensorflow.python.keras import backend
  from tensorflow.python.keras.engine import base_layer_utils
  from tensorflow.python.keras.engine.base_layer import Layer
  from tensorflow.python.keras.utils import tf_utils
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import array_ops_stack
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import nn
label_desc: Use image node_id 2 for calling the _Merge obj's underlying member method code with example usage: obj._merge_function(inputs) without return types