Fix #948: parseString errors with custom enum types

[facontidavide]

Summary

• Fix null pointer dereference on config().enums when parseString is called before enums are registered
• Fix enum types with convertFromString specializations not being called
• Three-level fallback: scripting enums registry -> numeric via from_chars -> convertFromString

Test plan

• New test: Enums.ParseEnumWithConvertFromString_Issue948
• All existing tests pass (298/298)

Closes #948

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/issue-948

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[RithwikU]

When will this PR #1075 (enum parsing fix) be included in ROS apt packages?

Hi @facontidavide,

Thank you for merging PR #1075 which fixes the enum parsing issues! This addresses exactly the problem we're encountering.

Our situation:

• We're using ROS 2 Jazzy with ros-jazzy-behaviortree-cpp from apt
• Current installed version: 4.8.3-1noble.20260126.192859 (built Jan 26, 2026)
• Issue: Enum types registered with registerScriptingEnums cannot be parsed from XML when assigned via the := operator (e.g., throw_side:=LEFT fails with type mismatch errors)
• PR Fix #948: parseString errors with custom enum types #1075 was merged Feb 1, 2026, which is after the 4.8.3 build

Question: When can we expect PR #1075 to be included in the ros-jazzy-behaviortree-cpp apt packages?

Will it be in:

• A 4.8.x patch release?
• A 4.9.0 release?
• Should we build from source in the meantime?

Understanding the timeline will help us decide whether to implement a workaround (custom convertFromString specialization) or wait for the apt package update.

Thanks for maintaining this excellent library!