small bugfix for bond graph traversal

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +2.66 :tada:

Comparison is base (fcb224d) 92.41% compared to head (b288b4b) 95.07%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #258 +/- ## ========================================== + Coverage 92.41% 95.07% +2.66% ========================================== Files 320 320 Lines 20042 20040 -2 ========================================== + Hits 18521 19054 +533 + Misses 1521 986 -535 ``` | Flag | Coverage Δ | | |---|---|---| | _shrug_Testing_CPU | `89.56% <100.00%> (-0.01%)` | :arrow_down: | | _shrug_Testing_CPU_w_o_jit | `91.52% <100.00%> (-0.01%)` | :arrow_down: | | _shrug_Testing_CUDA | `92.22% <100.00%> (+2.66%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=uw-ipd#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://app.codecov.io/gh/uw-ipd/tmol/pull/258?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=uw-ipd) | Coverage Δ | | |---|---|---| | [tmol/tests/optimization/test\_modules.py](https://app.codecov.io/gh/uw-ipd/tmol/pull/258?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=uw-ipd#diff-dG1vbC90ZXN0cy9vcHRpbWl6YXRpb24vdGVzdF9tb2R1bGVzLnB5) | `100.00% <ø> (ø)` | | | [tmol/chemical/restypes.py](https://app.codecov.io/gh/uw-ipd/tmol/pull/258?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=uw-ipd#diff-dG1vbC9jaGVtaWNhbC9yZXN0eXBlcy5weQ==) | `94.71% <100.00%> (ø)` | | ... and [25 files with indirect coverage changes](https://app.codecov.io/gh/uw-ipd/tmol/pull/258/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=uw-ipd)

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