message: clippy: use is_empty() instead of  len() == 0 (warn(len_zero)).
diff: @@ -1198,7 +1198,7 @@ impl Config {
  let mut f = fs::File::open(path)?;
  let mut contents = String::new();
  f.read_to_string(&mut contents)?;
  - if contents.len() == 0 {
  + if contents.is_empty() {
  return Err(Error::Empty);
  }
  