When creating a website measurable, we want to make sure at least one URL is always defined. However, since site URLs can be specified by plugin setting, it's possible to omit the 'urls' plugin setting entirely, or just send the name, eg, ['name' => 'urls'] instead of ['name' => 'urls', 'values' => ...]. In these cases, Matomo just ignores the setting entirely, never checking it or setting it to anything.

Having no site URL causes features like Overlay to break, so we should require them. However, some measurables legitimately have no URLs (like RollUps).