a1822d21d0
<!-- Thank you for the PR! Please go through the checklist below and make sure you've completed all the steps. Please review the [CONTRIBUTING.md](https://github.com/payloadcms/payload/blob/main/CONTRIBUTING.md) document in this repository if you haven't already. The following items will ensure that your PR is handled as smoothly as possible: - PR Title must follow conventional commits format. For example, `feat: my new feature`, `fix(plugin-seo): my fix`. - Minimal description explained as if explained to someone not immediately familiar with the code. - Provide before/after screenshots or code diffs if applicable. - Link any related issues/discussions from GitHub or Discord. - Add review comments if necessary to explain to the reviewer the logic behind a change ### What? ### Why? ### How? Fixes # --> ### What? This PR fixes an issue where the bottom "Create new ..." button would cause a runtime error due to not accounting for a polymorphic join setup. ### Why? To prevent a runtime error and allow users the ability to add new documents to the join as expected even in a polymorphic setup. ### How? Creation of a new `AddNewButton` which handles all of the add new button instances in the `RelationshipTable` component. Addresses https://github.com/payloadcms/payload/issues/12913#issuecomment-3001475438 Before: [join-polymorphic-runtime-error--Payload.webm](https://github.com/user-attachments/assets/fad3a1ba-c51c-4731-84cc-c27adbaac1d9) After: [polymorphic-after-Editing---Multiple-Collections-Parent---Payload (1).webm](https://github.com/user-attachments/assets/e3baf902-1b2b-4f19-8b6d-838edd6fef80)