Fix fatal error when requesting RSS format (#10407)

* Fixes #10399

* add test reproducing issue #10399

* another health check

core/DataTable/Renderer/Rss.php

@@ -64,9 +64,13 @@ class Rss extends Renderer
 
             $pudDate = date('r', $timestamp);
 
-            $dateInSiteTimezone = Date::factory($timestamp)->setTimezone($site->getTimezone())->toString('Y-m-d');
+            $dateInSiteTimezone = Date::factory($timestamp);
+            if($site) {
+                $dateInSiteTimezone = $dateInSiteTimezone->setTimezone($site->getTimezone());
+            }
+            $dateInSiteTimezone = $dateInSiteTimezone->toString('Y-m-d');
             $thisPiwikUrl = Common::sanitizeInputValue($piwikUrl . "&date=$dateInSiteTimezone");
-            $siteName = $site->getName();
+            $siteName = $site ? $site->getName() : '';
             $title = $siteName . " on " . $date;
 
             $out .= "\t<item>

plugins/MultiSites/tests/Integration/MultiSitesTest.php

@@ -9,6 +9,7 @@
 namespace Piwik\Plugins\MultiSites\tests\Integration;
 
 use Piwik\Access;
+use Piwik\FrontController;
 use Piwik\Plugins\MultiSites\API as APIMultiSites;
 use Piwik\Plugins\SitesManager\API as APISitesManager;
 use Piwik\Tests\Framework\TestCase\IntegrationTestCase;
@@ -49,4 +50,28 @@ class MultiSitesTest extends IntegrationTestCase
         // safety net
         $this->assertEquals(0, $dataTable->getFirstRow()->getColumn('nb_visits'));
     }
+
+    /**
+     * Testing that getOne does not error out when format=rss, #10407
+     *
+     * @group Plugins
+     */
+    public function testWhenRssFormatGetOneDoesNotError()
+    {
+        $_GET = array(
+            'method' => 'MultiSites.getOne',
+            'idSite' => $this->idSiteAccess,
+            'period' => 'month',
+            'date'   => 'last10',
+            'format'   => 'rss'
+        );
+
+        $output = FrontController::getInstance()->fetchDispatch('API');
+
+        $this->assertContains('<item>', $output);
+        $this->assertContains('</rss>', $output);
+        $this->assertNotContains('error', $output);
+
+        $_GET = array();
+    }
 }