year WrongNumberOfDigits

[Eloitor]

From https://mathscinet.ams.org/mathscinet/article?mr=4279905 I got the following bibtex:

@book{MR4279905,
  author    = {Voight, John},
  title     = {Quaternion algebras},
  series    = {Graduate Texts in Mathematics},
  volume    = {288},
  publisher = {Springer, Cham},
  year      = {[2021] \copyright 2021},
  pages     = {xxiii+885},
  isbn      = {978-3-030-56692-0; 978-3-030-56694-4},
  mrclass   = {11R52 (11-02 11E12 11F06 16H05 16U60 20H10)},
  mrnumber  = {4279905},
  mrreviewer= {Juliusz\ Brzezi\'nski},
  doi       = {10.1007/978-3-030-56694-4},
  url       = {https://doi.org/10.1007/978-3-030-56694-4},
}
EOF

hayagriva voight.bib > out.yaml

The output is

thread 'main' panicked at /Users/eloi/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hayagriva-0.8.1/src/main.rs:236:80:
called `Result::unwrap()` on an `Err` value: [Type(TypeError { span: 199..199, kind: WrongNumberOfDigits })]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[PgBiel]

Well, I suppose the error is correct, we can't really parse that year. But maybe this is some special syntax to indicate actual value vs how it should be displayed? Is there information on how we should parse this?