Incremental Interface adding Clauses to an empty solver causes undefined behavior

[XeroOl]

Create a project:

cargo new repro
cd repro
cargo add splr --features incremental_solver

Write code that adds clauses incrementally; not from a .cnf file:

use splr::{SatSolverIF, SolveIF, Solver};

fn main() {
    let mut s = Solver::default();
    for _ in 0..3 {
        s.add_var();
    }
    s.add_clause([1, 2]).unwrap();
    s.add_clause([1, 3]).unwrap();
    s.add_clause([2, 3]).unwrap();
    s.add_clause([-1, -2, -3]).unwrap();
    println!("{:?}", s.solve().unwrap());
}

run the code:

cargo run

I would expect something like Certificate::SAT([1, 2, -3]), but instead, I get a debug assertion:

thread 'main' panicked at library/core/src/panicking.rs:225:5:
unsafe precondition(s) violated: NonZero::new_unchecked requires the argument to be non-zero

This indicates a bug in the program. This Undefined Behavior check is optional, and cannot be relied on for safety.
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/3e674b06b5c74adea662bd0b0b06450757994b16/library/std/src/panicking.rs:697:5
   1: core::panicking::panic_nounwind_fmt::runtime
             at /rustc/3e674b06b5c74adea662bd0b0b06450757994b16/library/core/src/panicking.rs:117:22
   2: core::panicking::panic_nounwind_fmt
             at /rustc/3e674b06b5c74adea662bd0b0b06450757994b16/library/core/src/intrinsics/mod.rs:3174:9
   3: core::panicking::panic_nounwind
             at /rustc/3e674b06b5c74adea662bd0b0b06450757994b16/library/core/src/panicking.rs:225:5
   4: core::num::nonzero::NonZero<T>::new_unchecked::precondition_check
             at /home/xerool/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ub_checks.rs:68:21
   5: core::num::nonzero::NonZero<T>::new_unchecked
             at /home/xerool/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ub_checks.rs:75:17
   6: splr::cdb::cid::<impl core::convert::From<usize> for splr::cdb::ClauseId>::from
             at /home/xerool/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/splr-0.17.2/src/cdb/cid.rs:26:31
   7: splr::cdb::db::<impl splr::cdb::ClauseDBIF for splr::cdb::ClauseDB>::new_clause
             at /home/xerool/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/splr-0.17.2/src/cdb/db.rs:292:19
   8: splr::solver::build::<impl splr::solver::Solver>::add_unchecked_clause
             at /home/xerool/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/splr-0.17.2/src/solver/build.rs:310:18
   9: <splr::solver::Solver as splr::solver::build::SatSolverIF>::add_clause
             at /home/xerool/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/splr-0.17.2/src/solver/build.rs:211:12
  10: repro::main
             at ./src/main.rs:8:5
  11: core::ops::function::FnOnce::call_once
             at /home/xerool/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
thread caused non-unwinding panic. aborting.