code: def mult_aff(A, B):
      """Returns the matrix product A.dot(B) considering None as the identity
  
      Parameters
      ----------
      A : array, shape (n,k)
      B : array, shape (k,m)
  
      Returns
      -------
      The matrix product A.dot(B). If any of the input matrices is None, it is
      treated as the identity matrix. If both matrices are None, None is returned
      """
      if A is None:
          return B
      elif B is None:
          return A
      return A.dot(B)
  
imports: import logging
  import abc
  import numpy
  import numpy.linalg
  import nibabel
  from nibabel.streamlines import ArraySequence
  from dipy.align import vector_fields
  from dipy.align import floating
  from dipy.align import VerbosityLevels
  from dipy.align import Bunch
  from dipy.align.scalespace import ScaleSpace
label_desc: Use image node_id 1 for calling a global function with example usage: mult_aff(A, B) and returns: A, B, A