fix(skyline): guard against invalid input

[aem-code-sync[bot]]

Hello, I'm the AEM Code Sync Bot and I will run some actions to deploy your branch and validate page speed. In case there are problems, just click a checkbox below to rerun the respective action.

• [ ] Re-run PSI checks
• [ ] Re-sync branch

Commits

* [80c2a1b](https://github.com/adobe/helix-website/commit/80c2a1be7fa01f4dac774f8b7a1dca13445fa2f3) :white_check_mark: (latest) * [09d8e75](https://github.com/adobe/helix-website/commit/09d8e753a2003bcd7f62d46b92afa2249471367e) :white_check_mark: * [12db306](https://github.com/adobe/helix-website/commit/12db306f2dacb13f7a3782bb7859a0b184959014) :white_check_mark: