[FIX] Resolving a few SS4 things that were missed during the upgrade.

.upgrade.yml

@@ -0,0 +1,24 @@
+mappings:
+  MultisitesCMSMainExtension: 'Symbiote\Multisites\Admin\MultisitesCMSMainExtension'
+  MultisitesCMSPageAddController: 'Symbiote\Multisites\Admin\MultisitesCMSPageAddController'
+  MultisitesModelAdminExtension: 'Symbiote\Multisites\Admin\MultisitesModelAdminExtension'
+  MultisitesFrontController: 'Symbiote\Multisites\Control\MultisitesFrontController'
+  MultisitesRootController: 'Symbiote\Multisites\Control\MultisitesRootController'
+  RobotsTxtController: 'Symbiote\Multisites\Control\RobotsTxtController'
+  MultisitesAware: 'Symbiote\Multisites\Extension\MultisitesAware'
+  MultisitesContentControllerExtension: 'Symbiote\Multisites\Extension\MultisitesContentControllerExtension'
+  MultisitesControllerExtension: 'Symbiote\Multisites\Extension\MultisitesControllerExtension'
+  MultisitesErrorPageExtension: 'Symbiote\Multisites\Extension\MultisitesErrorPageExtension'
+  MultisitesFileFieldExtension: 'Symbiote\Multisites\Extension\MultisitesFileFieldExtension'
+  MultisitesHtmlEditorField_ToolbarExtension: 'Symbiote\Multisites\Extension\MultisitesHtmlEditorField_ToolbarExtension'
+  MultisitesMemberExtension: 'Symbiote\Multisites\Extension\MultisitesMemberExtension'
+  MultisitesReport: 'Symbiote\Multisites\Extension\MultisitesReport'
+  MultisitesSecurityExtension: 'Symbiote\Multisites\Extension\MultisitesSecurityExtension'
+  MultisitesSiteConfigExtension: 'Symbiote\Multisites\Extension\MultisitesSiteConfigExtension'
+  MultisitesSiteTreeExtension: 'Symbiote\Multisites\Extension\MultisitesSiteTreeExtension'
+  SiteSearchForm: 'Symbiote\Multisites\Form\SiteSearchForm'
+  MultisitesInitAssetsTask: 'Symbiote\Multisites\Job\MultisitesInitAssetsTask'
+  TidySiteTask: 'Symbiote\Multisites\Job\TidySiteTask'
+  Site: 'Symbiote\Multisites\Model\Site'
+  Multisites: 'Symbiote\Multisites\Multisites'
+  MultisiteSiteTest: 'Symbiote\Multisites\Tests\MultisiteSiteTest'

_config/upgrade.yml

@@ -0,0 +1,6 @@
+---
+name: multisites-upgrade
+---
+SilverStripe\ORM\DatabaseAdmin:
+  classname_value_remapping:
+    Site: 'Symbiote\Multisites\Model\Site'

src/Extension/MultisitesControllerExtension.php

@@ -81,7 +81,7 @@ public function onBeforeHTTPError($code, $request)
         if ($errorPage) {
             Requirements::clear();
             Requirements::clear_combined_files();
-            $response = ModelAsController::controller_for($errorPage)->handleRequest($request, DataModel::inst());
+            $response = ModelAsController::controller_for($errorPage)->handleRequest($request);
             throw new HTTPResponse_Exception($response, $code);
         }
     }

src/Model/Site.php

@@ -182,7 +182,7 @@ public function onBeforeWrite() {
 
 		$this->Host = $normalise($this->Host);
 
-		if($aliases = $this->HostAliases->getValue()) {
+		if(!is_array($this->HostAliases) && ($aliases = $this->HostAliases->getValue())) {
 			$this->HostAliases = array_map($normalise, $aliases);
 		}