Preserve omitted additionalProperties

[ChiragAgg5k]

Keep an omitted additionalProperties distinct from an explicit true. Both permit unknown properties according to OpenAPI semantics, but downstream consumers may need to preserve whether the keyword was present.\n\n- use null for an omitted keyword\n- retain explicit booleans and typed schemas\n- cover omitted and explicit-open object schemas\n\ncomposer test and composer check pass.

[greptile-apps]

Greptile Summary

The PR preserves the distinction between an omitted additionalProperties keyword and an explicit true.

• Makes ObjectSchema::$additionalProperties nullable and defaults it to null.
• Updates schema parsing to retain omission while preserving booleans and typed schemas.
• Adds reader coverage for omitted and explicitly open object schemas.

Confidence Score: 5/5

The PR appears safe to merge with no concrete changed-code failure identified.

The parser and model consistently preserve omission as null, explicit values retain their prior representations, and no repository consumer mishandles the new nullable state.

Important Files Changed

Filename	Overview
src/Model/Schema/ObjectSchema.php	Extends the public property type with null and changes its default to represent an omitted keyword.
src/Parser/Schema/Reader.php	Preserves omission as null while continuing to parse explicit booleans and schema-valued additionalProperties.
tests/Schema/ReaderTest.php	Adds focused assertions distinguishing omitted additionalProperties from explicit true.

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