code: def concatenate_not_none(l, axis=0):
      
      # Get the indexes of the arrays in the list
      mask = []
      for i in range(len(l)):
          if l[i] is not None:
              mask.append(i)
  
      # Concatenate them
      l_stacked = np.concatenate([l[i] for i in mask], axis=axis)
      return l_stacked
docs: Construct a numpy array by stacking not-None arrays in a list
  
      Parameters
      ----------
  
      data : list of arrays
          The list of arrays to be concatenated. Arrays have same shape in all
          but one dimension or are None, in which case they are ignored.
  
      axis : int, default = 0
          Axis for the concatenation
  
  
      Returns
      -------
  
      data_stacked : array
          The resulting concatenated array.