Add test and fix bug.

module/VuFind/src/VuFind/MetadataVocabulary/AbstractBase.php

@@ -60,9 +60,9 @@ abstract class AbstractBase implements MetadataVocabularyInterface
         return [
             'author' => array_unique(
                 array_merge(
-                    $driver->tryMethod('getPrimaryAuthors'),
-                    $driver->tryMethod('getSecondaryAuthors'),
-                    $driver->tryMethod('getCorporateAuthors')
+                    $driver->tryMethod('getPrimaryAuthors') ?? [],
+                    $driver->tryMethod('getSecondaryAuthors') ?? [],
+                    $driver->tryMethod('getCorporateAuthors') ?? []
                 )
             ),
             'container_title' => $driver->tryMethod('getContainerTitle'),

module/VuFind/tests/unit-tests/src/VuFindTest/View/Helper/Root/MetadataTest.php

+<?php
+/**
+ * Metadata Test Class
+ *
+ * PHP version 7
+ *
+ * Copyright (C) Villanova University 2020.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * @category VuFind
+ * @package  Tests
+ * @author   Demian Katz <demian.katz@villanova.edu>
+ * @license  http://opensource.org/licenses/gpl-2.0.php GNU General Public License
+ * @link     https://vufind.org/wiki/development:testing:unit_tests Wiki
+ */
+namespace VuFindTest\View\Helper\Root;
+
+use VuFind\MetadataVocabulary\PluginManager;
+use VuFind\MetadataVocabulary\PRISM;
+use VuFind\View\Helper\Root\Metadata;
+use VuFindTest\RecordDriver\TestHarness;
+use Zend\Config\Config;
+use Zend\View\Helper\HeadMeta;
+
+/**
+ * Metadata Test Class
+ *
+ * @category VuFind
+ * @package  Tests
+ * @author   Demian Katz <demian.katz@villanova.edu>
+ * @license  http://opensource.org/licenses/gpl-2.0.php GNU General Public License
+ * @link     https://vufind.org/wiki/development:testing:unit_tests Wiki
+ */
+class MetadataTest extends \VuFindTest\Unit\TestCase
+{
+    /**
+     * Get a fake record driver
+     *
+     * @param array $data Test data
+     *
+     * @return TestHarness
+     */
+    protected function getDriver($data)
+    {
+        $driver = new TestHarness();
+        $driver->setRawData($data);
+        return $driver;
+    }
+
+    /**
+     * Get a mock HeadMeta helper
+     *
+     * @return HeadMeta
+     */
+    protected function getMetaHelper()
+    {
+        $mock = $this->getMockBuilder(HeadMeta::class)
+            ->disableOriginalConstructor()
+            ->setMethods(['appendName'])
+            ->getMock();
+        $mock->expects($this->once())->method('appendName')
+            ->with($this->equalTo('prism.title'), $this->equalTo('Fake Title'));
+        return $mock;
+    }
+
+    /**
+     * Get a mock plugin manager
+     *
+     * @return PluginManager
+     */
+    protected function getPluginManager()
+    {
+        $mock = $this->getMockBuilder(PluginManager::class)
+            ->disableOriginalConstructor()
+            ->setMethods(['get'])
+            ->getMock();
+        $mock->expects($this->once())->method('get')
+            ->with($this->equalTo('PRISM'))
+            ->will($this->returnValue(new PRISM()));
+        return $mock;
+    }
+
+    /**
+     * Test basic functionality of the helper.
+     *
+     * @return void
+     */
+    public function testMetadata()
+    {
+        $helper = new Metadata(
+            $this->getPluginManager(),
+            new Config(['Vocabularies' => [TestHarness::class => ['PRISM']]]),
+            $this->getMetaHelper()
+        );
+        $helper->generateMetatags(
+            $this->getDriver(['Title' => 'Fake Title'])
+        );
+    }
+}