I have a database where for whatever unknown reason a Landing page refers to an non-existing block.

How that inconsistency might happend in the first place is a separate issue. However, If (when) that happens, the application will not deal with it gracefully. Instead you'll get an exception and a 500 result.

Expected results:

• The rest of the page should be rendered as expected.
• Possibly writing a message on the page that one block could not be fetched ( there are pros/cons regarding that)
• Log the error