diff --git a/src/Entity/Index.php b/src/Entity/Index.php
index 6fc0752..fb6bb03 100644
--- a/src/Entity/Index.php
+++ b/src/Entity/Index.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\search_api\Entity;
 
+use Drupal\Component\Plugin\Exception\PluginException;
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Config\Entity\ConfigEntityBase;
@@ -155,7 +156,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *
    * @see getTrackerInstance()
    */
-  protected $trackerInstance = FALSE;
+  protected $trackerInstance = NULL;
 
   /**
    * The ID of the server on which data should be indexed.
@@ -352,8 +353,8 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function hasValidTracker() {
-    $tracker = $this->getTrackerInstance();
-    return ($tracker instanceof TrackerInterface);
+    return (bool) \Drupal::service('plugin.manager.search_api.tracker')
+      ->getDefinition($this->getTrackerId(), FALSE);
   }
 
   /**
@@ -361,10 +362,10 @@ class Index extends ConfigEntityBase implements IndexInterface {
    */
   public function getTrackerId() {
     $settings = $this->getTrackerSettings();
-    if ($settings === array()) {
-      return 'default';
+    if (!$settings) {
+      return \Drupal::config('search_api.settings')->get('default_tracker');
     }
-    $tracker_settings = array_values($settings)[0];
+    $tracker_settings = reset($settings);
     return $tracker_settings['plugin_id'];
   }
 
@@ -372,10 +373,6 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function getTrackerInstance() {
-    if ($this->getTrackerSettings() === NULL) {
-      return NULL;
-    }
-
     if (!$this->trackerInstance) {
       if ($this->getTrackerSettings() === array()) {
         $tracker_settings = array(
@@ -507,15 +504,19 @@ class Index extends ConfigEntityBase implements IndexInterface {
       $processor_settings = $this->getProcessorSettings();
 
       foreach ($processor_plugin_manager->getDefinitions() as $name => $processor_definition) {
-        if (class_exists($processor_definition['class']) && empty($this->processorInstances[$name])) {
+        if (empty($this->processorInstances[$name])) {
           // Create our settings for this processor.
           $settings = empty($processor_settings[$name]['settings']) ? array() : $processor_settings[$name]['settings'];
           $settings['index'] = $this;
 
           /** @var $processor \Drupal\search_api\Processor\ProcessorInterface */
-          $processor = $processor_plugin_manager->createInstance($name, $settings);
-          if ($processor->supportsIndex($this)) {
-            $this->processorInstances[$name] = $processor;
+          try {
+            $processor = $processor_plugin_manager->createInstance($name, $settings);
+            if ($processor->supportsIndex($this)) {
+              $this->processorInstances[$name] = $processor;
+            }
+          } catch (PluginException $e) {
+            \Drupal::logger('search_api')->warning('Processor @id specifies a non-existing @class.', array('@id' => $name, '@class' => $processor_definition['class']));
           }
         }
         elseif (!class_exists($processor_definition['class'])) {
@@ -802,16 +803,13 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function indexSpecificItems(array $search_objects) {
-    if (!$search_objects) {
-      return array();
-    }
-    if ($this->isReadOnly()) {
+    if (!$search_objects || $this->isReadOnly()) {
       return array();
     }
     if (!$this->status()) {
       throw new SearchApiException(new FormattableMarkup("Couldn't index values on index %index (index is disabled)", array('%index' => $this->label())));
     }
-    if (empty($this->getFields())) {
+    if (!$this->getFields()) {
       throw new SearchApiException(new FormattableMarkup("Couldn't index values on index %index (no fields selected)", array('%index' => $this->label())));
     }
 
diff --git a/src/Form/IndexForm.php b/src/Form/IndexForm.php
index 3885dfd..accb9b0 100644
--- a/src/Form/IndexForm.php
+++ b/src/Form/IndexForm.php
@@ -262,7 +262,7 @@ class IndexForm extends EntityForm {
       '#title' => $this->t('Tracker'),
       '#description' => $this->t('Select the type of tracker which should be used for keeping track of item changes.'),
       '#options' => $this->getTrackerPluginManager()->getOptionsList(),
-      '#default_value' => !$index->isNew() && $index->hasValidTracker() ? $index->getTrackerInstance()->getPluginId() : key($tracker_options),
+      '#default_value' => $index->hasValidTracker() ? $index->getTrackerId() : key($tracker_options),
       '#required' => TRUE,
       '#disabled' => !$index->isNew(),
       '#ajax' => array(
diff --git a/tests/src/Kernel/LanguageKernelTest.php b/tests/src/Kernel/LanguageKernelTest.php
index b555e77..dacdc3e 100644
--- a/tests/src/Kernel/LanguageKernelTest.php
+++ b/tests/src/Kernel/LanguageKernelTest.php
@@ -104,12 +104,23 @@ class LanguageKernelTest extends KernelTestBase {
     $this->server->save();
 
     // Create a test index.
+    $datasource_id = 'entity:' . $this->testEntityTypeId;
     $this->index = Index::create(array(
       'name' => 'Test Index',
       'id' => 'test_index',
       'status' => 1,
-      'datasources' => array('entity:' . $this->testEntityTypeId),
-      'tracker' => 'default',
+      'datasource_settings' => array(
+        $datasource_id => array(
+          'plugin_id' => $datasource_id,
+          'settings' => array(),
+        ),
+      ),
+      'tracker_settings' => array(
+        'default'=> array(
+          'plugin_id' => 'default',
+          'settings' => array(),
+        ),
+      ),
       'server' => $this->server->id(),
       'options' => array('index_directly' => FALSE),
     ));