Empty 'License details' field error doesn't have descriptive error message

[Cody A.W. Somerville]

If you edit a project and it has 'Other/Proprietary' selected as a license but you leave 'License details' empty then you'll be brought back to the edit details page upon clicking 'Change'. The problem is that the page jumps to Licenses section but the error message 'There is 1 error.' is at the top of the page so there is no visible indication of an error. Since the licenses section is so close to the bottom of the page I initially thought nothing was happening when I submitted the form due to not paying close attention.

Furthermore, the project in question had an empty license details field to start with. I know that the project was created via a launchpadlib script so it seems that error checking is inconsistent (or has changed since but I suspect it hasn't).