fix(parse): ignore undefined options so defaults are preserved

[abhu85]

Problem

Closes #1160.

ParserOptions declares optional fields with defaults, then does Object.assign(this, opts). Because Object.assign copies enumerable undefined values, explicitly passing an optional option as undefined overwrites its default. For delimiter this then throws:

new ParserOptions({ delimiter: undefined });
// TypeError: Cannot read properties of undefined (reading 'length')
//   at new ParserOptions (.../ParserOptions.ts:73)  // this.delimiter.length

The options type marks every field optional (delimiter?: string), so passing undefined should be equivalent to omitting it — i.e. fall back to the default , — not blow up. This bites anyone forwarding options that themselves default to undefined.

Fix

Filter out undefined entries before assigning, so defaults declared on the class are preserved:

const definedOpts = Object.entries(opts || {}).filter(([, value]) => {
    return value !== undefined;
});
Object.assign(this, Object.fromEntries(definedOpts));

This is general (any explicitly-undefined option now falls back to its default) and changes nothing for callers passing real values.

Test plan

• Added ParserOptions test: { delimiter: undefined } resolves to the default ,.
• New test fails on main with the reported TypeError; passes with the fix.
• jest packages/parse — 373 passing, no regressions.
• eslint --max-warnings 0 and prettier --check clean on the changed files.