def convert(tree,fileName=None):
  """
    Converts input files to be compatible with merge request #460:
     - Removes "all" node
     - Sets default variable names
    @ In, tree, xml.etree.ElementTree.ElementTree object, the contents of a RAVEN input file
    @ In, fileName, the name for the raven input file
    @Out, tree, xml.etree.ElementTree.ElementTree object, the modified RAVEN input file
  """
  simulation = tree.getroot()
  opts = simulation.find('Optimizers')
  if opts is not None:
    for child in opts:
      if child.tag == 'FiniteDifferenceGradientOptimizer':
        child.tag = 'FiniteDifference'
  return tree