Preserve empty URL segment metadata handling without requiring URL prefix

plugins/Actions/DataTable/Filter/Actions.php

@@ -93,11 +93,11 @@ public function filter($table)
                                 $row->setMetadata('segmentValue', urlencode(trim($label)));
                             }
                         }
-                    } elseif ($this->actionType == Action::TYPE_PAGE_URL && $urlPrefix) { // folder for older data w/ no folder URL metadata
+                    } elseif ($this->actionType == Action::TYPE_PAGE_URL) { // folder for older data w/ no folder URL metadata
                         if ($label === $notDefinedUrl) {
                             // segmenting by an "empty" value is currently broken for actions, so we do not set a segment value to hide row actions like segmented visit log
                             $row->setMetadata('segment', null);
-                        } else {
+                        } elseif ($urlPrefix) {
                             $row->setMetadata('segment', 'pageUrl=^' . urlencode(urlencode($urlPrefix . '/' . $label)));
                         }
                     }

plugins/Actions/tests/Unit/DataTableFilterActionsTest.php

@@ -0,0 +1,54 @@
+<?php
+
+/**
+ * Matomo - free/libre analytics platform
+ *
+ * @link    https://matomo.org
+ * @license https://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ */
+
+namespace Piwik\Plugins\Actions\tests\Unit;
+
+use Piwik\DataTable;
+use Piwik\DataTable\Row;
+use Piwik\Plugins\Actions\ArchivingHelper;
+use Piwik\Plugins\Actions\DataTable\Filter\Actions as ActionsFilter;
+use Piwik\Tests\Framework\Fixture;
+use Piwik\Tracker\Action;
+
+require_once PIWIK_INCLUDE_PATH . '/plugins/Actions/Actions.php';
+
+/**
+ * @group Actions
+ * @group DataTableFilterActionsTest
+ * @group Plugins
+ */
+class DataTableFilterActionsTest extends \PHPUnit\Framework\TestCase
+{
+    public function setUp(): void
+    {
+        Fixture::loadAllTranslations();
+    }
+
+    public function tearDown(): void
+    {
+        Fixture::resetTranslations();
+    }
+
+    public function testFilterSetsNullSegmentForUnknownPageUrlEvenWithoutSiteUrlPrefix()
+    {
+        ArchivingHelper::reloadConfig();
+
+        $table = new DataTable();
+        $notDefinedUrl = ArchivingHelper::getUnknownActionName(Action::TYPE_PAGE_URL);
+        $row = new Row([Row::COLUMNS => ['label' => $notDefinedUrl]]);
+        $table->addRow($row);
+
+        $filter = new ActionsFilter($table, Action::TYPE_PAGE_URL);
+        $filter->filter($table);
+
+        $allMetadata = $row->getMetadata();
+        $this->assertArrayHasKey('segment', $allMetadata);
+        $this->assertNull($allMetadata['segment']);
+    }
+}