reported in https://forum.matomo.org/t/the-address-is-not-a-valid-url/47725 and reproduced on 4.12.0
If e.g. the "Global list of excluded referrers" is empty, the form can't be saved:
related to #19302
This issue has been mentioned on Matomo forums. There might be relevant details there:
on all installations after update the same problem!
Quickly did a PR for this one, just wondering, once the global setting is successfully saved, should we show a success notification on the top?