Fix regression on optional regex submatches

[ala-ableton]

Summary

Fixes a regression that was introduced in commit a7ff906 (Regex: use iterators for match results).

Details

Until commit a7ff906, the vector returned by RegexMatch::getSubmatches() contained an empty string item for each optional submatch that didn't match. Commit a7ff906 broke that behavior by skipping any submatch that didn't match.

How Has This Been Tested?

I added a test (matchesRegexWithOptionalSubmatches) to tests/unit/RegexTest.cpp.
I cherry-picked this test on top of 4dec371 (the parent commit of a7ff906) and verified that it was passing. I then verified that this test doesn't pass on top of the latest master without the corresponding change in src/Regex.cpp.

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Checklist:

• It is my own work, its copyright is implicitly assigned to the project and no substantial part of it has been copied from other sources (including Stack Overflow). In rare occasions this is acceptable, like in CMake modules where the original copyright information should be kept.
• I'm using the same code standards as the existing code (indentation, spacing, variable naming, ...).
• I've added tests for my code.
• I have verified whether my change requires changes to the documentation
• My change either requires no documentation change or I've updated the documentation accordingly.
• My branch has been rebased to master, keeping only relevant commits.

[ala-ableton]

I have no clue about whether I should make any changes to the documentation (including CHANGELOG.md), so I left the 2 check boxes un-ticked for now.

[coveralls]

Coverage increased (+0.01%) to 62.47% when pulling e7b8f64 on AbletonAppDev:fix-regression-on-optional-regex-submatches into ee740d2 on cucumber:master.

[ala-ableton]

Following the recent merges of #216 and #215, I've rebased and force-pushed my branch.
@muggenhor, @paoloambrosio: please review, thanks!

[muggenhor]

Thanks for your PR, this looks good!

[ala-ableton]

@muggenhor: thank you for the review! Can you take care of merging this PR, or should we wait for @paoloambrosio to also have a look?

[muggenhor]

I'll probablyintend to merge it somewhere later this week

[paoloambrosio]

I'm late to the party, but top quality PR! 👍

[aslakhellesoy]

Hi @ala-ableton,

Thanks for your making your first contribution to Cucumber, and welcome to the Cucumber committers team! You can now push directly to this repo and all other repos under the cucumber organization! 🍾

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