Constant lexical_write_float::format::REQUIRED_DIGITS

pub const REQUIRED_DIGITS: u128 = REQUIRED_INTEGER_DIGITS | REQUIRED_FRACTION_DIGITS | REQUIRED_EXPONENT_DIGITS
    | REQUIRED_MANTISSA_DIGITS; // 0x0000_0000_0000_0000_0000_0000_0000_000fu128

At least 1 digit in the number is required.