When you send to trash content, that was previously selected in Content List Block in Landing Page, user won't be able to view/edit said Landing Page anymore, with exception:

Twig_Error_Runtime:
An exception has been thrown during the rendering of a template ("Unsupported value (NULL)").

That comes from:

InvalidArgumentException:
Unsupported value (NULL)

Steps to reproduce:
1. Create Article: "Test Article". Publish it.
2. Create Landing Page: "Test Landing Page".
3. Add Content List Block to it, select previously created "Test Article". Publish Landing Page.
4. Send "Test Article" to tash.
5. View "Test Landing Page".

Result:
An exception has been thrown during the rendering of a template ("Unsupported value (NULL)").

Exception:
The page will load normally with some kind information for Content List Block that content is in the trash.