This plugin has 2 commands, /enableportals and /disable portals.
If portals are disabled, the PlayerPortalEvent is simply canceled. If they are enabled with the command, then it will not be canceled.
I personally wanted to allow End Gateways, but if you do not want to, then simply remove the if statement at line 43 and put the contents in the if (portalUsageEnabled) statement.
This plugin is far from perfect, so if you are actively using it and are annoyed with a bug, open an issue and I will resolve it :)