[reginaldalfret]

Fixes #320

Summary

Fixes an issue where implicit null scalars within flow mappings (such as a: {b: } or GitHub Actions workflow dispatch blocks on: { push: { branches: [main] }, workflow_dispatch: }) were converted into empty single-quoted strings '' (e.g. a: {b: ''}).

Root Cause

In pkg/yaml/emitterc.go, an empty scalar node was marked with flow_plain_allowed = false and len == 0 && emitter.flow_level > 0 unconditionally forced style = yaml_SINGLE_QUOTED_SCALAR_STYLE. This caused implicit null values in flow mappings to fall back to single-quoted empty strings ''.

Changes

1. Set emitter.scalar_data.flow_plain_allowed = true for empty scalar values in yaml_emitter_analyze_scalar.
2. Changed the condition in yaml_emitter_select_scalar_style from len(value) == 0 && (emitter.flow_level > 0 || emitter.simple_key_context) to only check len(value) == 0 && emitter.simple_key_context.
3. Fixed stripTrailingNewline in formatter_test.go to properly strip CRLF endings.
4. Added test cases in pkg/yaml/node_test.go (TestFlowMappingImplicitNull) and formatters/basic/formatter_test.go.