At the top of the theme show page we have a link
to the theme About and License, which are supposed
to be URLs. However some themes have left placeholder
text in these metadata fields, which leads to a wonky
experience.
Instead, we can just not serialize these fields if they
are not valid URLs, then they will not show as links
in the UI.
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction