docs: @Nonnull
    public DescribeCommand abbrev(@Nullable Integer n) {
      if (n != null) {
        Preconditions.checkArgument(n < 41, String.format("N (commit abbrev length) must be < 41. (Was:[%s])", n));
        Preconditions.checkArgument(n >= 0, String.format("N (commit abbrev length) must be positive! (Was [%s])", n));
        log.info("--abbrev = {}", n);
        abbrev = n;
      }
      return this;
    }