Get the nested value identified by the json path, rooted at source.

def get_json_val(source, path, *, ignore_bad_path=False):
  """Get the nested value identified by the json path, rooted at source."""
  try:
    return JP.find(source, path)
  except JP.JSONPathError as ex:
    if ignore_bad_path:
      return None
    else:
      raise