code: def _aggr_sum(inList):
    
    aggrMean = _aggr_mean(inList)
    if aggrMean == None:
      return None
  
    aggrSum = 0
    for elem in inList:
      if elem != SENTINEL_VALUE_FOR_MISSING_DATA:
        aggrSum += elem
      else:
        aggrSum += aggrMean
  
    return aggrSum
docs: Returns sum of the elements in the list. Missing items are replaced with
    the mean value