<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def migrate_value(value):
 """Convert `value` to a new-style value, if necessary and possible. An "old-style" value is a value that uses any `value` field other than the `tensor` field. A "new-style" value is a value that uses the `tensor` field. TensorBoard continues to support old-style values on disk; this method converts them to new-style values so that further code need only deal with one data format. Arguments: value: A `Summary.Value` object. This argument is not modified. Returns: If the `value` is an old-style value for which there is a new-style equivalent, the result is the new-style value. Otherwise---if the value is already new-style or does not yet have a new-style equivalent---the value will be returned unchanged. :type value: Summary.Value :rtype: Summary.Value """

  handler = {
      'histo': _migrate_histogram_value,
      'image': _migrate_image_value,
      'audio': _migrate_audio_value,
      'simple_value': _migrate_scalar_value,
  }.get(value.WhichOneof('value'))
  return handler(value) if handler else value