Issue #2632314 by alexpott, amateescu, ivanjaros: PluginSettingsBase::getThirdPartySettings() returns null instead of array

core/lib/Drupal/Core/Field/PluginSettingsBase.php

@@ -99,7 +99,7 @@ abstract class PluginSettingsBase extends PluginBase implements PluginSettingsIn
    */
   public function getThirdPartySettings($module = NULL) {
     if ($module) {
-      return isset($this->thirdPartySettings[$module]) ? $this->thirdPartySettings[$module] : NULL;
+      return isset($this->thirdPartySettings[$module]) ? $this->thirdPartySettings[$module] : [];
     }
     return $this->thirdPartySettings;
   }

core/tests/Drupal/Tests/Core/Field/PluginSettingsBaseTest.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Field\PluginSettingsBaseTest.
+ */
+
+namespace Drupal\Tests\Core\Field;
+
+use Drupal\Core\Field\PluginSettingsBase;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Field\PluginSettingsBase
+ * @group Field
+ */
+class PluginSettingsBaseTest extends UnitTestCase {
+
+  /**
+   * @covers ::getThirdPartySettings
+   */
+  public function testGetThirdPartySettings() {
+    $plugin_settings = new TestPluginSettingsBase();
+    $this->assertSame([], $plugin_settings->getThirdPartySettings());
+    $this->assertSame([], $plugin_settings->getThirdPartySettings('test'));
+    $plugin_settings->setThirdPartySetting('test', 'foo', 'bar');
+    $this->assertSame(['foo' => 'bar'], $plugin_settings->getThirdPartySettings('test'));
+    $this->assertSame([], $plugin_settings->getThirdPartySettings('test2'));
+  }
+
+}
+
+class TestPluginSettingsBase extends PluginSettingsBase {
+
+  public function __construct() {
+  }
+
+}