diff --git a/src/Entity/Index.php b/src/Entity/Index.php
index bf01515..e9d6886 100644
--- a/src/Entity/Index.php
+++ b/src/Entity/Index.php
@@ -199,7 +199,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *
    * @see loadProcessors()
    */
-  protected $processorInstances;
+  protected $processorInstances = NULL;
 
   /**
    * Whether reindexing has been triggered for this index in this page request.
@@ -491,8 +491,8 @@ class Index extends ConfigEntityBase implements IndexInterface {
       'settings' => $processor->getConfiguration(),
     );
 
-    // Reset processors static cache.
-    $this->processorInstances = array();
+    // Reset processors canonical storage.
+    $this->processorInstances = NULL;
 
     return $this;
   }
@@ -503,8 +503,8 @@ class Index extends ConfigEntityBase implements IndexInterface {
   public function removeProcessor($processor_id) {
     unset($this->processor_settings[$processor_id]);
 
-    // Reset processors static cache.
-    $this->processorInstances = array();
+    // Reset processors canonical storage.
+    $this->processorInstances = NULL;
 
     return $this;
   }
@@ -516,7 +516,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *   The loaded processors, keyed by processor ID.
    */
   protected function loadProcessors() {
-    if (empty($this->processorInstances)) {
+    if (is_null($this->processorInstances)) {
       /** @var $processor_plugin_manager \Drupal\search_api\Processor\ProcessorPluginManager */
       $processor_plugin_manager = \Drupal::service('plugin.manager.search_api.processor');
       $processor_settings = $this->processor_settings;
diff --git a/src/Tests/Processor/ProcessorIntegrationTest.php b/src/Tests/Processor/ProcessorIntegrationTest.php
index 1be986d..9519a62 100644
--- a/src/Tests/Processor/ProcessorIntegrationTest.php
+++ b/src/Tests/Processor/ProcessorIntegrationTest.php
@@ -50,65 +50,86 @@ class ProcessorIntegrationTest extends WebTestBase {
   public function testProcessorIntegration() {
     // By default, the add_url and language processors are already enabled.
     $enabled = array('add_url', 'language');
-    $this->assertEqual(sort($enabled), array_keys($this->loadIndex()->getProcessors()));
+    $this->assertEqual($enabled, array_keys($this->loadIndex()->getProcessors()));
 
     $this->checkContentAccessIntegration();
     $enabled[] = 'content_access';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkHighlightIntegration();
     $enabled[] = 'highlight';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkHtmlFilterIntegration();
     $enabled[] = 'html_filter';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkIgnoreCaseIntegration();
     $enabled[] = 'ignorecase';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkIgnoreCharactersIntegration();
     $enabled[] = 'ignore_character';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkNodeStatusIntegration();
     $enabled[] = 'node_status';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkRenderedItemIntegration();
     $enabled[] = 'rendered_item';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkStopWordsIntegration();
     $enabled[] = 'stopwords';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkTokenizerIntegration();
     $enabled[] = 'tokenizer';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     $this->checkTransliterationIntegration();
     $enabled[] = 'transliteration';
+    sort($enabled);
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
 
     // The 'language' and 'add_url' processors are are not available to be removed
     $actual_processors = array_keys($this->loadIndex()->getProcessors());
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    sort($actual_processors);
+    $this->assertEqual($enabled, $actual_processors);
     $this->checkLanguageIntegration();
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    $this->assertEqual($enabled, $actual_processors);
     $this->checkUrlFieldIntegration();
-    $this->assertEqual(sort($enabled), sort($actual_processors));
+    $this->assertEqual($enabled, $actual_processors);
   }
 
   /**
diff --git a/tests/src/Kernel/DependencyRemovalTest.php b/tests/src/Kernel/DependencyRemovalTest.php
index 745f379..641d0e9 100644
--- a/tests/src/Kernel/DependencyRemovalTest.php
+++ b/tests/src/Kernel/DependencyRemovalTest.php
@@ -87,13 +87,13 @@ class DependencyRemovalTest extends KernelTestBase {
    * If the dependency does not get removed, proper cascading to the index is
    * also verified.
    *
-   * @param bool $dependency_removal_return_value
+   * @param bool $remove_dependency
    *   Whether to remove the dependency from the backend when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testBackendDependency($dependency_removal_return_value) {
+  public function testBackendDependency($remove_dependency) {
     $dependency_key = $this->dependency->getConfigDependencyKey();
     $dependency_name = $this->dependency->getConfigDependencyName();
 
@@ -133,7 +133,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_backend\Plugin\search_api\backend\TestBackend::onDependencyRemoval().
     $key = 'search_api_test_backend.dependencies.remove';
-    \Drupal::state()->set($key, $dependency_removal_return_value);
+    \Drupal::state()->set($key, $remove_dependency);
 
     // Delete the backend's dependency.
     $this->dependency->delete();
@@ -147,7 +147,7 @@ class DependencyRemovalTest extends KernelTestBase {
     $storage->resetCache();
     $server = $storage->load($server->id());
 
-    if ($dependency_removal_return_value) {
+    if ($remove_dependency) {
       $this->assertInstanceOf('Drupal\search_api\ServerInterface', $server, 'Server was not removed');
       $this->assertArrayNotHasKey('dependencies', $server->get('backend_config'), 'Backend config was adapted');
       // @todo Logically, this should not be changed: if the server does not get
@@ -169,13 +169,13 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Tests a datasource with a dependency that gets removed.
    *
-   * @param bool $dependency_removal_return_value
+   * @param bool $remove_dependency
    *   Whether to remove the dependency from the datasource when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testDatasourceDependency($dependency_removal_return_value) {
+  public function testDatasourceDependency($remove_dependency) {
     // Add the datasource to the index and save it. The datasource configuration
     // contains the dependencies it will return – in our case, we use the test
     // server.
@@ -207,7 +207,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_dependencies\Plugin\search_api\datasource\TestDatasource::onDependencyRemoval().
     $key = 'search_api_test_dependencies.datasource.remove';
-    \Drupal::state()->set($key, $dependency_removal_return_value);
+    \Drupal::state()->set($key, $remove_dependency);
 
     // Delete the datasource's dependency.
     $this->dependency->delete();
@@ -224,13 +224,12 @@ class DependencyRemovalTest extends KernelTestBase {
     // Depending on whether the plugin should have removed the dependency or
     // not, make sure the right action was taken.
     $datasources = $this->index->get('datasource_settings');
-    if ($dependency_removal_return_value) {
-      $this->assertContains('search_api_test_dependencies', array_keys($datasources), 'Datasource not removed');
+    if ($remove_dependency) {
+      $this->assertArrayHasKey('search_api_test_dependencies', $datasources, 'Datasource not removed');
       $this->assertEmpty($datasources['search_api_test_dependencies']['settings'], 'Datasource settings adapted');
     }
     else {
-      $this->assertNotContains('search_api_test_dependencies', array_keys($datasources), 'Datasource removed');
-      $this->assertArrayNotHasKey('search_api_test_dependencies', $datasources, 'Datasource config removed');
+      $this->assertArrayNotHasKey('search_api_test_dependencies', $datasources, 'Datasource removed');
     }
   }
 
@@ -273,13 +272,13 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Tests a processor with a dependency that gets removed.
    *
-   * @param bool $dependency_removal_return_value
+   * @param bool $remove_dependency
    *   Whether to remove the dependency from the processor when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testProcessorDependency($dependency_removal_return_value) {
+  public function testProcessorDependency($remove_dependency) {
     // Add the processor to the index and save it. The processor configuration
     // contains the dependencies it will return – in our case, we use the test
     // server.
@@ -305,7 +304,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_dependencies\Plugin\search_api\processor\TestProcessor::onDependencyRemoval().
     $key = 'search_api_test_dependencies.processor.remove';
-    \Drupal::state()->set($key, $dependency_removal_return_value);
+    \Drupal::state()->set($key, $remove_dependency);
 
     // Delete the processor's dependency.
     $this->dependency->delete();
@@ -322,7 +321,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // Depending on whether the plugin should have removed the dependency or
     // not, make sure the right action was taken.
     $processors = $this->index->get('processor_settings');
-    if ($dependency_removal_return_value) {
+    if ($remove_dependency) {
       $this->assertArrayHasKey('search_api_test_dependencies', $processors, 'Processor not removed');
       $this->assertEmpty($processors['search_api_test_dependencies']['settings'], 'Processor settings adapted');
     }
@@ -334,13 +333,13 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Tests a tracker with a dependency that gets removed.
    *
-   * @param bool $dependency_removal_return_value
+   * @param bool $remove_dependency
    *   Whether to remove the dependency from the tracker when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testTrackerDependency($dependency_removal_return_value) {
+  public function testTrackerDependency($remove_dependency) {
     // Set the tracker for the index and save it. The tracker configuration
     // contains the dependencies it will return – in our case, we use the test
     // server.
@@ -366,10 +365,10 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_dependencies\Plugin\search_api\tracker\TestTracker::onDependencyRemoval().
     $key = 'search_api_test_dependencies.tracker.remove';
-    \Drupal::state()->set($key, $dependency_removal_return_value);
+    \Drupal::state()->set($key, $remove_dependency);
     // If the index resets the tracker, it needs to know the ID of the default
     // tracker.
-    if (!$dependency_removal_return_value) {
+    if (!$remove_dependency) {
       \Drupal::configFactory()->getEditable('search_api.settings')
         ->set('default_tracker', 'default')
         ->save();
@@ -393,7 +392,7 @@ class DependencyRemovalTest extends KernelTestBase {
     $plugins = array_keys($config);
     $tracker = $config[$plugins[0]]['plugin_id'];
     $tracker_config = $config[$plugins[0]]['settings'];
-    if ($dependency_removal_return_value) {
+    if ($remove_dependency) {
       $this->assertEquals('search_api_test_dependencies', $tracker, 'Tracker not reset');
       $this->assertEmpty($tracker_config, 'Tracker settings adapted');
     }
@@ -461,16 +460,15 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Data provider for this class's test methods.
    *
-   * If $dependency_removal_return_value is TRUE, in
-   * Plugin::onDependencyRemoval() it clears its configuration (and thus its
-   * dependency, in those test plugins) and returns TRUE, which the index will
-   * take as "all OK, dependency removed" and leave the plugin where it is, only
-   * with updated configuration.
+   * If $remove_dependency is TRUE, in Plugin::onDependencyRemoval() it clears
+   * its configuration (and thus its dependency, in those test plugins) and
+   * returns TRUE, which the index will take as "all OK, dependency removed" and
+   * leave the plugin where it is, only with updated configuration.
    *
-   * If $dependency_removal_return_value is FALSE, Plugin::onDependencyRemoval()
-   * will do nothing and just return FALSE, the index says "oh, that plugin
-   * still has that removed dependency, so I should better remove the plugin"
-   * and the plugin gets removed.
+   * If $remove_dependency is FALSE, Plugin::onDependencyRemoval() will do
+   * nothing and just return FALSE, the index says "oh, that plugin still has
+   * that removed dependency, so I should better remove the plugin" and the
+   * plugin gets removed.
    *
    * @return array
    *   An array of argument arrays for this class's test methods.