trim leading dots from extensions and drop any empty strings.

def __trim_extensions_dot(exts):
  """trim leading dots from extensions and drop any empty strings."""
  if exts is None:
    return None
  res = []
  for i in range(0, len(exts)):
    if exts[i] == "":
      continue
    res.append(__trim_extension_dot(exts[i]))
  return res