#203 - Fix ProcessState::addErrorContextValue() TypeError on empty iterables and PropertySetterTask

[njoubert-cleverage]

Description

Fixes #203.

ProcessState::addErrorContextValue() only accepts string|int|array values. When a task passes any other value (null, bool, float, object), a \TypeError is thrown and the real behaviour or error is lost:

• Iterable tasks on an empty iterable (ConstantIterableOutputTask, InputIteratorTask, YamlReaderTask with {}/[], SplitJoinLineTask with no line to produce): AbstractIterableOutputTask::execute() always adds iterator_key before checking the iterator. On an empty iterator key() is null, so the process fails instead of skipping the task, as documented.
• PropertySetterTask: when a value cannot be set, the task adds the value to the error context. If that value is a bool, float, null or object, the TypeError replaces the original exception (e.g. NoSuchPropertyException).

This PR:

• Widen the $value parameter of ProcessState::addErrorContextValue() to mixed.
• In AbstractIterableOutputTask::execute(), add iterator_key only when the iterator is valid: an empty iterable then produces no output and the task is skipped.
• Update the reference documentation (property_setter_task.md, yaml_reader_task.md, split_join_line_task.md, 03-custom_tasks.md), add unit tests.

The new regression tests fail on main and pass with this fix. PHPUnit, PHPStan, PHP-CS-Fixer and Rector pass.

Requirements

• Documentation updates
  • Reference
  • Cookbooks
  • Changelog
• Unit tests

Breaking changes

None for callers. Widening a parameter type is backward compatible, except for a subclass of ProcessState overriding addErrorContextValue() with the old signature (it must widen $value to mixed).

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