fix(experimental): allow null with optional and default: null

[ping-maxwell]

Summary

• optional: true accepts null as well as undefined (types + validate)
• default: null is valid on all schema helpers; absence produces null without type-checking it as the field type

Test plan

• pnpm test in packages/experimental
• v.string({ optional: true, default: null }) typechecks and validates omit/null → null

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/better-call@201

commit: 33a60da

[greptile-apps]

Greptile Summary

The PR updates the experimental schema system so optional fields accept null and all schema helpers support null defaults, aligning related function-schema and capability types.

• Adds null-aware input and output inference for optional and defaulted schemas.
• Returns null defaults without validating them as the schema's underlying field type.
• Expands runtime and compile-time coverage across primitive, object, array, union, and function schemas.

Confidence Score: 4/5

The null-default input contract should be corrected before merging because callers can pass an explicitly permitted null that runtime validation rejects.

Non-optional schemas with default: null now infer null as valid caller input, but the validator only substitutes defaults for undefined or optional null, leaving explicit null to fail the underlying type check.

Files Needing Attention: packages/experimental/src/schema.ts, packages/experimental/src/schema-dx.test.ts

_{Reviews (1): Last reviewed commit: "Merge branch 'experimental' into experim..." | Re-trigger Greptile}

[greptile-apps]

Null input contract diverges

When a caller explicitly passes null to a non-optional schema with default: null, InferArgs accepts the call but validate does not apply the default and throws a validation error. For example, { n: null } type-checks for v.object({ n: v.number({ default: null }) }) but fails at runtime with expected number, received null.

Knowledge Base Used: Validation and schema contracts