Sanitize page.get GraphQL variables for JSON-safe SSR responses

[Copilot]

---

name: Pull Request
about: Give us some information about your proposed PR
title: ''
assignees: ''

Proposed Changes

page.get() was returning undefined optional GraphQL variables in the response metadata, which breaks strict JSON serialization in Next.js Pages Router SSR/SSG. This update keeps the outbound GraphQL request unchanged while making returned graphql.variables safe to serialize.

• Return-path sanitization
  • omit undefined keys from graphql.variables before attaching them to successful page.get() responses and DotErrorPage.graphql
• Request behavior preserved
  • keep existing request construction and default core variables (url, mode, languageId, fireRules, siteId) intact
  • continue passing through provided optional variables (personaId, publishDate, variantName) when explicitly set
• Regression coverage
  • update existing page client expectations to reflect omitted undefined optionals
  • add coverage that returned graphql.variables contains no undefined values and survives JSON round-trip

Checklist

• Tests
• Translations
• Security Implications Contemplated (add notes if applicable)

Additional Info

Returned metadata now behaves like:

const result = await dotCMSClient.page.get('/');

result.graphql.variables;
// before: { url: '/', mode: 'LIVE', languageId: '1', fireRules: false, siteId: '...', personaId: undefined, publishDate: undefined, variantName: undefined }
// after:  { url: '/', mode: 'LIVE', languageId: '1', fireRules: false, siteId: '...' }

No request-side behavior is intentionally changed; the fix is limited to the response/error GraphQL metadata exposed to consumers.

Screenshots

Original	Updated
N/A	N/A