diff --git a/modules/jsonapi/jsonapi.module b/modules/jsonapi/jsonapi.module
index 70648d2..df5bc5c 100644
--- a/modules/jsonapi/jsonapi.module
+++ b/modules/jsonapi/jsonapi.module
@@ -18,15 +18,9 @@ function jsonapi_help($route_name, RouteMatchInterface $route_match) {
   switch ($route_name) {
     case 'help.page.jsonapi':
       $output = '<h3>' . t('About') . '</h3>';
-      $youtube_url = Url::fromUri('https://www.youtube.com/playlist?list=PLZOQ_ZMpYrZsyO-3IstImK1okrpfAjuMZ', [
-        'external' => TRUE,
-      ]);
-      $youtube_link = Link::fromTextAndUrl(t('online documentation for the JSON API module'), $youtube_url);
-      $spec_url = Url::fromUri('http://jsonapi.org', ['external' => TRUE]);
-      $spec_link = Link::fromTextAndUrl(t('JSON API Specification'), $spec_url);
-      $output .= '<p>' . t('The JSON API module is a fully compliant implementation of the @spec. By following shared conventions, you can increase productivity, take advantage of generalized tooling, and focus on what matters: your application. Clients built around JSON API are able to take advantage of its features such as efficiently caching responses, sometimes eliminating network requests entirely. For more information, see the @online.', [
-          '@spec' => $spec_link->toString(),
-          '@online' => $youtube_link->toString(),
+      $output .= '<p>' . t('The JSON API module is a fully compliant implementation of the <a href=":spec">JSON API Specification</a>. By following shared conventions, you can increase productivity, take advantage of generalized tooling, and focus on what matters: your application. Clients built around JSON API are able to take advantage of its features such as efficiently caching responses, sometimes eliminating network requests entirely. For more information, see the <a href=":docs">online documentation for the JSON API module</a>.', [
+          ':spec' => 'http://jsonapi.org',
+          ':docs' => 'https://www.youtube.com/playlist?list=PLZOQ_ZMpYrZsyO-3IstImK1okrpfAjuMZ',
         ]) . '</p>';
       $output .= '<dl>';
       $output .= '<dt>' . t('General') . '</dt>';
diff --git a/modules/jsonapi/jsonapi.services.yml b/modules/jsonapi/jsonapi.services.yml
index 2804940..f42e648 100644
--- a/modules/jsonapi/jsonapi.services.yml
+++ b/modules/jsonapi/jsonapi.services.yml
@@ -1,4 +1,18 @@
 services:
+  serializer.normalizer.htt_exception.jsonapi:
+    class: Drupal\jsonapi\Normalizer\HttpExceptionNormalizer
+    arguments: ['@current_user']
+    tags:
+      - { name: normalizer, priority: 1 }
+  serializer.normalizer.unprocessable_entity_exception.jsonapi:
+    class: Drupal\jsonapi\Normalizer\UnprocessableHttpEntityExceptionNormalizer
+    arguments: ['@current_user']
+    tags:
+      - { name: normalizer, priority: 2 }
+  serializer.normalizer.scalar.jsonapi:
+    class: Drupal\jsonapi\Normalizer\ScalarNormalizer
+    tags:
+      - { name: normalizer, priority: 5 }
   serializer.normalizer.entity_reference_item.jsonapi:
     class: Drupal\jsonapi\Normalizer\RelationshipItemNormalizer
     arguments: ['@jsonapi.resource_type.repository', '@serializer.normalizer.jsonapi_document_toplevel.jsonapi',]
@@ -8,19 +22,10 @@ services:
     class: Drupal\jsonapi\Normalizer\FieldItemNormalizer
     tags:
       - { name: normalizer, priority: 21 }
-  serializer.normalizer.scalar.jsonapi:
-    class: Drupal\jsonapi\Normalizer\ScalarNormalizer
-    tags:
-      - { name: normalizer, priority: 5 }
   serializer.normalizer.field.jsonapi:
     class: Drupal\jsonapi\Normalizer\FieldNormalizer
     tags:
       - { name: normalizer, priority: 21 }
-  serializer.normalizer.entity_reference_field.jsonapi:
-    class: Drupal\jsonapi\Normalizer\EntityReferenceFieldNormalizer
-    arguments: ['@jsonapi.link_manager', '@entity_field.manager', '@plugin.manager.field.field_type', '@jsonapi.resource_type.repository', '@entity.repository']
-    tags:
-      - { name: normalizer, priority: 31 }
   serializer.normalizer.relationship.jsonapi:
     class: Drupal\jsonapi\Normalizer\RelationshipNormalizer
     arguments: ['@jsonapi.resource_type.repository', '@jsonapi.link_manager']
@@ -41,16 +46,11 @@ services:
     arguments: ['@jsonapi.link_manager', '@jsonapi.current_context', '@entity_type.manager']
     tags:
       - { name: normalizer, priority: 22 }
-  serializer.normalizer.htt_exception.jsonapi:
-    class: Drupal\jsonapi\Normalizer\HttpExceptionNormalizer
-    arguments: ['@current_user']
-    tags:
-      - { name: normalizer, priority: 1 }
-  serializer.normalizer.unprocessable_entity_exception.jsonapi:
-    class: Drupal\jsonapi\Normalizer\UnprocessableHttpEntityExceptionNormalizer
-    arguments: ['@current_user']
+  serializer.normalizer.entity_reference_field.jsonapi:
+    class: Drupal\jsonapi\Normalizer\EntityReferenceFieldNormalizer
+    arguments: ['@jsonapi.link_manager', '@entity_field.manager', '@plugin.manager.field.field_type', '@jsonapi.resource_type.repository', '@entity.repository']
     tags:
-      - { name: normalizer, priority: 2 }
+      - { name: normalizer, priority: 31 }
   serializer.encoder.jsonapi:
     class: Drupal\jsonapi\Encoder\JsonEncoder
     tags:
diff --git a/modules/jsonapi/src/Access/CustomParameterNames.php b/modules/jsonapi/src/Access/CustomParameterNames.php
index 7a89c56..a8ec382 100644
--- a/modules/jsonapi/src/Access/CustomParameterNames.php
+++ b/modules/jsonapi/src/Access/CustomParameterNames.php
@@ -33,6 +33,8 @@ class CustomParameterNames implements AccessInterface {
   /**
    * Validates the JSONAPI parameters.
    *
+   * @see http://jsonapi.org/format/#document-member-names-reserved-characters
+   *
    * @param string[] $json_api_params
    *   The JSONAPI parameters.
    *
@@ -42,7 +44,7 @@ class CustomParameterNames implements AccessInterface {
     $valid = TRUE;
 
     foreach (array_keys($json_api_params) as $name) {
-      if (strpbrk($name, '+,.[]!”#$%&’()*/:;<=>?@^`{}~|')) {
+      if (strpbrk($name, "+,.[]!”#$%&’()*/:;<=>?@\\^`{}~|\x0\x1\x2\x3\x4\x5\x6\x7\x8\x9\xA\xB\xC\xD\xE\xF\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1A\x1B\x1C\x1D\x1E\x1F")) {
         $valid = FALSE;
         break;
       }
diff --git a/modules/jsonapi/src/Context/CurrentContext.php b/modules/jsonapi/src/Context/CurrentContext.php
index bc3370d..bcd42a1 100644
--- a/modules/jsonapi/src/Context/CurrentContext.php
+++ b/modules/jsonapi/src/Context/CurrentContext.php
@@ -97,12 +97,11 @@ class CurrentContext {
    *   The JSON API provided parameter.
    */
   public function getJsonApiParameter($parameter_key) {
-    $params = $this
+    return $this
       ->requestStack
       ->getCurrentRequest()
       ->attributes
-      ->get('_json_api_params');
-    return (isset($params[$parameter_key])) ? $params[$parameter_key] : NULL;
+      ->get("_json_api_params[$parameter_key]", NULL, TRUE);
   }
 
   /**
diff --git a/modules/jsonapi/src/Context/FieldResolver.php b/modules/jsonapi/src/Context/FieldResolver.php
index b2adcd3..9eab90d 100644
--- a/modules/jsonapi/src/Context/FieldResolver.php
+++ b/modules/jsonapi/src/Context/FieldResolver.php
@@ -3,7 +3,7 @@
 namespace Drupal\jsonapi\Context;
 
 use Drupal\Core\Entity\EntityFieldManagerInterface;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 
 /**
  * Service which resolves public field names to and from Drupal field names.
diff --git a/modules/jsonapi/src/Controller/EntityResource.php b/modules/jsonapi/src/Controller/EntityResource.php
index eab187e..907171b 100644
--- a/modules/jsonapi/src/Controller/EntityResource.php
+++ b/modules/jsonapi/src/Controller/EntityResource.php
@@ -18,8 +18,8 @@ use Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem;
 use Drupal\jsonapi\Resource\EntityCollection;
 use Drupal\jsonapi\Resource\JsonApiDocumentTopLevel;
 use Drupal\jsonapi\ResourceType\ResourceType;
-use Drupal\jsonapi\Error\SerializableHttpException;
-use Drupal\jsonapi\Error\UnprocessableHttpEntityException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
+use Drupal\jsonapi\Exception\UnprocessableHttpEntityException;
 use Drupal\jsonapi\Query\QueryBuilder;
 use Drupal\jsonapi\Context\CurrentContext;
 use Drupal\jsonapi\ResourceResponse;
@@ -129,7 +129,7 @@ class EntityResource {
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   The entity object.
    *
-   * @throws \Drupal\jsonapi\Error\SerializableHttpException
+   * @throws \Drupal\jsonapi\Exception\SerializableHttpException
    *   If validation errors are found.
    */
   protected function validate(EntityInterface $entity) {
@@ -248,8 +248,8 @@ class EntityResource {
     // Instantiate the query for the filtering.
     $entity_type_id = $this->resourceType->getEntityTypeId();
 
-    $params = $request->attributes->get('_route_params');
-    $query = $this->getCollectionQuery($entity_type_id, $params['_json_api_params']);
+    $params = $request->attributes->get('_route_params[_json_api_params]', NULL, TRUE);
+    $query = $this->getCollectionQuery($entity_type_id, $params);
 
     $results = $query->execute();
 
@@ -644,8 +644,11 @@ class EntityResource {
     // The update is different for configuration entities and content entities.
     if ($origin instanceof ContentEntityInterface && $destination instanceof ContentEntityInterface) {
       // First scenario: both are content entities.
-      if (!$destination_field_list = $destination->get($field_name)) {
-        throw new SerializableHttpException(400, sprintf('The provided field (%s) does not exist in the entity with ID %d.', $field_name, $destination->id()));
+      try {
+        $destination_field_list = $destination->get($field_name);
+      }
+      catch (\Exception $e) {
+        throw new SerializableHttpException(400, sprintf('The provided field (%s) does not exist in the entity with ID %s.', $field_name, $destination->uuid()));
       }
 
       $origin_field_list = $origin->get($field_name);
@@ -675,9 +678,7 @@ class EntityResource {
    *   Returns TRUE, if entity field is EntityReferenceItem.
    */
   protected function isRelationshipField($entity_field) {
-    /** @var \Drupal\Core\Field\FieldTypePluginManager $field_type_manager */
-    $field_type_manager = \Drupal::service('plugin.manager.field.field_type');
-    $class = $field_type_manager->getPluginClass($entity_field->getDataDefinition()->getType());
+    $class = $this->pluginManager->getPluginClass($entity_field->getDataDefinition()->getType());
     return ($class == EntityReferenceItem::class || is_subclass_of($class, EntityReferenceItem::class));
   }
 
diff --git a/modules/jsonapi/src/Controller/RequestHandler.php b/modules/jsonapi/src/Controller/RequestHandler.php
index c4616b0..c318b5a 100644
--- a/modules/jsonapi/src/Controller/RequestHandler.php
+++ b/modules/jsonapi/src/Controller/RequestHandler.php
@@ -7,7 +7,7 @@ use Drupal\Core\Render\RenderContext;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\jsonapi\Context\CurrentContext;
 use Drupal\jsonapi\Error\ErrorHandler;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Drupal\jsonapi\ResourceResponse;
 use Symfony\Component\DependencyInjection\ContainerAwareInterface;
 use Symfony\Component\DependencyInjection\ContainerAwareTrait;
diff --git a/modules/jsonapi/src/EventSubscriber/DefaultExceptionSubscriber.php b/modules/jsonapi/src/EventSubscriber/DefaultExceptionSubscriber.php
index 55c1a8d..fb21a3e 100644
--- a/modules/jsonapi/src/EventSubscriber/DefaultExceptionSubscriber.php
+++ b/modules/jsonapi/src/EventSubscriber/DefaultExceptionSubscriber.php
@@ -2,7 +2,7 @@
 
 namespace Drupal\jsonapi\EventSubscriber;
 
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Drupal\serialization\EventSubscriber\DefaultExceptionSubscriber as SerializationDefaultExceptionSubscriber;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
diff --git a/modules/jsonapi/src/Error/SerializableHttpException.php b/modules/jsonapi/src/Exception/SerializableHttpException.php
similarity index 87%
rename from modules/jsonapi/src/Error/SerializableHttpException.php
rename to modules/jsonapi/src/Exception/SerializableHttpException.php
index 91b0732..3aaa117 100644
--- a/modules/jsonapi/src/Error/SerializableHttpException.php
+++ b/modules/jsonapi/src/Exception/SerializableHttpException.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\jsonapi\Error;
+namespace Drupal\jsonapi\Exception;
 
 use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 use Symfony\Component\HttpKernel\Exception\HttpException;
diff --git a/modules/jsonapi/src/Error/UnprocessableHttpEntityException.php b/modules/jsonapi/src/Exception/UnprocessableHttpEntityException.php
similarity index 97%
rename from modules/jsonapi/src/Error/UnprocessableHttpEntityException.php
rename to modules/jsonapi/src/Exception/UnprocessableHttpEntityException.php
index 032a382..7730f5f 100644
--- a/modules/jsonapi/src/Error/UnprocessableHttpEntityException.php
+++ b/modules/jsonapi/src/Exception/UnprocessableHttpEntityException.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\jsonapi\Error;
+namespace Drupal\jsonapi\Exception;
 
 use Drupal\Core\Entity\EntityConstraintViolationListInterface;
 
diff --git a/modules/jsonapi/src/LinkManager/LinkManager.php b/modules/jsonapi/src/LinkManager/LinkManager.php
index b8875ed..b3f6d03 100644
--- a/modules/jsonapi/src/LinkManager/LinkManager.php
+++ b/modules/jsonapi/src/LinkManager/LinkManager.php
@@ -4,7 +4,7 @@ namespace Drupal\jsonapi\LinkManager;
 
 use Drupal\Core\Routing\UrlGeneratorInterface;
 use Drupal\jsonapi\ResourceType\ResourceType;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Drupal\jsonapi\Routing\Param\OffsetPage;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
 use Symfony\Component\HttpFoundation\Request;
@@ -97,7 +97,7 @@ class LinkManager {
    * @param array $link_context
    *   An associative array with extra data to build the links.
    *
-   * @throws \Drupal\jsonapi\Error\SerializableHttpException
+   * @throws \Drupal\jsonapi\Exception\SerializableHttpException
    *   When the offset and size are invalid.
    *
    * @return string[]
diff --git a/modules/jsonapi/src/Normalizer/EntityNormalizer.php b/modules/jsonapi/src/Normalizer/EntityNormalizer.php
index f052198..7958248 100644
--- a/modules/jsonapi/src/Normalizer/EntityNormalizer.php
+++ b/modules/jsonapi/src/Normalizer/EntityNormalizer.php
@@ -9,7 +9,7 @@ use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Field\EntityReferenceFieldItemList;
 use Drupal\jsonapi\Normalizer\Value\EntityNormalizerValue;
 use Drupal\jsonapi\ResourceType\ResourceType;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Drupal\jsonapi\LinkManager\LinkManager;
 use Drupal\jsonapi\Normalizer\Value\NullFieldNormalizerValue;
 use Drupal\jsonapi\ResourceType\ResourceTypeRepository;
diff --git a/modules/jsonapi/src/Normalizer/EntityReferenceFieldNormalizer.php b/modules/jsonapi/src/Normalizer/EntityReferenceFieldNormalizer.php
index 9ca2095..bdddd71 100644
--- a/modules/jsonapi/src/Normalizer/EntityReferenceFieldNormalizer.php
+++ b/modules/jsonapi/src/Normalizer/EntityReferenceFieldNormalizer.php
@@ -9,7 +9,7 @@ use Drupal\Core\Field\FieldTypePluginManagerInterface;
 use Drupal\Core\Field\TypedData\FieldItemDataDefinition;
 use Drupal\jsonapi\ResourceType\ResourceTypeRepository;
 use Drupal\jsonapi\Resource\EntityCollection;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Drupal\jsonapi\LinkManager\LinkManager;
 use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
 
diff --git a/modules/jsonapi/src/Normalizer/NormalizerBase.php b/modules/jsonapi/src/Normalizer/NormalizerBase.php
index 46c3496..5447661 100644
--- a/modules/jsonapi/src/Normalizer/NormalizerBase.php
+++ b/modules/jsonapi/src/Normalizer/NormalizerBase.php
@@ -27,14 +27,14 @@ abstract class NormalizerBase extends SerializationNormalizerBase {
    * {@inheritdoc}
    */
   public function supportsNormalization($data, $format = NULL) {
-    return in_array($format, $this->formats) && parent::supportsNormalization($data, $format);
+    return in_array($format, $this->formats, TRUE) && parent::supportsNormalization($data, $format);
   }
 
   /**
    * {@inheritdoc}
    */
   public function supportsDenormalization($data, $type, $format = NULL) {
-    if (in_array($format, $this->formats) && (class_exists($this->supportedInterfaceOrClass) || interface_exists($this->supportedInterfaceOrClass))) {
+    if (in_array($format, $this->formats, TRUE) && (class_exists($this->supportedInterfaceOrClass) || interface_exists($this->supportedInterfaceOrClass))) {
       $target = new \ReflectionClass($type);
       $supported = new \ReflectionClass($this->supportedInterfaceOrClass);
       if ($supported->isInterface()) {
diff --git a/modules/jsonapi/src/Normalizer/UnprocessableHttpEntityExceptionNormalizer.php b/modules/jsonapi/src/Normalizer/UnprocessableHttpEntityExceptionNormalizer.php
index 556defa..2326d81 100644
--- a/modules/jsonapi/src/Normalizer/UnprocessableHttpEntityExceptionNormalizer.php
+++ b/modules/jsonapi/src/Normalizer/UnprocessableHttpEntityExceptionNormalizer.php
@@ -3,7 +3,7 @@
 namespace Drupal\jsonapi\Normalizer;
 
 use Drupal\Core\Session\AccountProxyInterface;
-use Drupal\jsonapi\Error\UnprocessableHttpEntityException;
+use Drupal\jsonapi\Exception\UnprocessableHttpEntityException;
 use Symfony\Component\HttpKernel\Exception\HttpException;
 
 /**
@@ -37,7 +37,7 @@ class UnprocessableHttpEntityExceptionNormalizer extends HttpExceptionNormalizer
    * {@inheritdoc}
    */
   protected function buildErrorObjects(HttpException $exception) {
-    /** @var $exception \Drupal\jsonapi\Error\UnprocessableHttpEntityException */
+    /** @var $exception \Drupal\jsonapi\Exception\UnprocessableHttpEntityException */
     $errors = parent::buildErrorObjects($exception);
     $error = $errors[0];
     unset($error['links']);
diff --git a/modules/jsonapi/src/Normalizer/Value/JsonApiDocumentTopLevelNormalizerValue.php b/modules/jsonapi/src/Normalizer/Value/JsonApiDocumentTopLevelNormalizerValue.php
index ce9f46c..628c9d8 100644
--- a/modules/jsonapi/src/Normalizer/Value/JsonApiDocumentTopLevelNormalizerValue.php
+++ b/modules/jsonapi/src/Normalizer/Value/JsonApiDocumentTopLevelNormalizerValue.php
@@ -72,9 +72,7 @@ class JsonApiDocumentTopLevelNormalizerValue implements ValueExtractorInterface,
    */
   public function __construct(array $values, array $context, $is_collection = FALSE, array $link_context) {
     $this->values = $values;
-    array_walk($values, function ($value) {
-      $this->addCacheableDependency($value);
-    });
+    array_walk($values, [$this, 'addCacheableDependency']);
     // Make sure that different sparse fieldsets are cached differently.
     $this->addCacheableDependency(new RequestCacheabilityDependency());
 
@@ -90,9 +88,7 @@ class JsonApiDocumentTopLevelNormalizerValue implements ValueExtractorInterface,
     }, $values);
     // Flatten the includes.
     $this->includes = array_reduce($this->includes, function ($carry, $includes) {
-      array_walk($includes, function ($include) {
-        $this->addCacheableDependency($include);
-      });
+      array_walk($includes, [$this, 'addCacheableDependency']);
       return array_merge($carry, $includes);
     }, []);
     // Filter the empty values.
diff --git a/modules/jsonapi/src/Query/GroupOption.php b/modules/jsonapi/src/Query/GroupOption.php
index 050ba63..d51a20c 100644
--- a/modules/jsonapi/src/Query/GroupOption.php
+++ b/modules/jsonapi/src/Query/GroupOption.php
@@ -146,11 +146,7 @@ class GroupOption implements QueryOptionInterface, QueryOptionTreeItemInterface
     // If any child GroupOptions or their children have the id return TRUE.
     return array_reduce($this->groupOptions, function ($has_child, $group) use ($id) {
       // If we already know that we have the child, skip evaluation and return.
-      if (!$has_child) {
-        // Determine if this group or any of its children match the $id.
-        $has_child = ($group->id() == $id || $group->hasChild($id));
-      }
-      return $has_child;
+      return $has_child || $group->id() == $id || $group->hasChild($id);
     }, FALSE);
   }
 
diff --git a/modules/jsonapi/src/Query/QueryBuilder.php b/modules/jsonapi/src/Query/QueryBuilder.php
index f439aa5..0e84c03 100644
--- a/modules/jsonapi/src/Query/QueryBuilder.php
+++ b/modules/jsonapi/src/Query/QueryBuilder.php
@@ -4,7 +4,7 @@ namespace Drupal\jsonapi\Query;
 
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Drupal\jsonapi\Routing\Param\OffsetPage;
 use Drupal\jsonapi\Routing\Param\Filter;
 use Drupal\jsonapi\Routing\Param\JsonApiParamInterface;
diff --git a/modules/jsonapi/src/Resource/EntityCollection.php b/modules/jsonapi/src/Resource/EntityCollection.php
index beb1f08..d173abc 100644
--- a/modules/jsonapi/src/Resource/EntityCollection.php
+++ b/modules/jsonapi/src/Resource/EntityCollection.php
@@ -12,7 +12,7 @@ class EntityCollection implements \IteratorAggregate, \Countable {
   /**
    * Entity storage.
    *
-   * @var array
+   * @var \Drupal\Core\Entity\EntityInterface[]
    */
   protected $entities;
 
@@ -26,7 +26,7 @@ class EntityCollection implements \IteratorAggregate, \Countable {
   /**
    * Instantiates a EntityCollection object.
    *
-   * @param array $entities
+   * @param \Drupal\Core\Entity\EntityInterface[] $entities
    *   The entities for the collection.
    */
   public function __construct(array $entities) {
diff --git a/modules/jsonapi/src/Routing/Param/Filter.php b/modules/jsonapi/src/Routing/Param/Filter.php
index 3869db3..2033473 100644
--- a/modules/jsonapi/src/Routing/Param/Filter.php
+++ b/modules/jsonapi/src/Routing/Param/Filter.php
@@ -1,7 +1,7 @@
 <?php
 
 namespace Drupal\jsonapi\Routing\Param;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 
 /**
  * @internal
diff --git a/modules/jsonapi/src/Routing/Param/JsonApiParamInterface.php b/modules/jsonapi/src/Routing/Param/JsonApiParamInterface.php
index bb757aa..695aa37 100644
--- a/modules/jsonapi/src/Routing/Param/JsonApiParamInterface.php
+++ b/modules/jsonapi/src/Routing/Param/JsonApiParamInterface.php
@@ -10,6 +10,9 @@ interface JsonApiParamInterface {
   /**
    * The key name.
    *
+   * This must be redefined with a unique value in each class that extends
+   * from JsonApiParamInterface.
+   *
    * @var string
    */
   const KEY_NAME = NULL;
diff --git a/modules/jsonapi/src/Routing/Param/OffsetPage.php b/modules/jsonapi/src/Routing/Param/OffsetPage.php
index 2217e16..e2b3feb 100644
--- a/modules/jsonapi/src/Routing/Param/OffsetPage.php
+++ b/modules/jsonapi/src/Routing/Param/OffsetPage.php
@@ -1,7 +1,7 @@
 <?php
 
 namespace Drupal\jsonapi\Routing\Param;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 
 /**
  * @internal
diff --git a/modules/jsonapi/src/Routing/Param/Sort.php b/modules/jsonapi/src/Routing/Param/Sort.php
index 3e78b4e..e0aac10 100644
--- a/modules/jsonapi/src/Routing/Param/Sort.php
+++ b/modules/jsonapi/src/Routing/Param/Sort.php
@@ -2,7 +2,7 @@
 
 namespace Drupal\jsonapi\Routing\Param;
 
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 
 /**
  * @internal
diff --git a/modules/jsonapi/src/Routing/RouteEnhancer.php b/modules/jsonapi/src/Routing/RouteEnhancer.php
index b9844a0..9ee019d 100644
--- a/modules/jsonapi/src/Routing/RouteEnhancer.php
+++ b/modules/jsonapi/src/Routing/RouteEnhancer.php
@@ -3,7 +3,7 @@
 namespace Drupal\jsonapi\Routing;
 
 use Drupal\Core\Routing\Enhancer\RouteEnhancerInterface;
-use Drupal\jsonapi\Error\SerializableHttpException;
+use Drupal\jsonapi\Exception\SerializableHttpException;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Routing\Route;
diff --git a/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php b/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php
index 87fdadb..acfbf8d 100644
--- a/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php
+++ b/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php
@@ -668,7 +668,26 @@ class JsonApiFunctionalTest extends BrowserTestBase {
     $this->assertEquals("body.0.format: The value you selected is not a valid choice.", $updated_response['errors'][1]['detail']);
     $this->assertEquals("/data/attributes/title", $updated_response['errors'][0]['source']['pointer']);
     $this->assertEquals("/data/attributes/body/format", $updated_response['errors'][1]['source']['pointer']);
-    // 13. Successful DELETE.
+    // 13. PATCH with field that doesn't exist on Entity.
+    $body = [
+      'data' => [
+        'id' => $uuid,
+        'type' => 'node--article',
+        'attributes' => [
+          'field_that_doesnt_exist' => 'foobar',
+        ],
+      ],
+    ];
+    $response = $this->request('PATCH', $individual_url, [
+      'body' => Json::encode($body),
+      'auth' => [$this->user->getUsername(), $this->user->pass_raw],
+      'headers' => ['Content-Type' => 'application/vnd.api+json'],
+    ]);
+    $updated_response = Json::decode($response->getBody()->__toString());
+    $this->assertEquals(400, $response->getStatusCode());
+    $this->assertEquals("The provided field (field_that_doesnt_exist) does not exist in the entity with ID $uuid.",
+      $updated_response['errors']['0']['detail']);
+    // 14. Successful DELETE.
     $response = $this->request('DELETE', $individual_url, [
       'auth' => [$this->user->getUsername(), $this->user->pass_raw],
     ]);
diff --git a/modules/jsonapi/tests/src/Kernel/Controller/EntityResourceTest.php b/modules/jsonapi/tests/src/Kernel/Controller/EntityResourceTest.php
index aff2c58..93e8609 100644
--- a/modules/jsonapi/tests/src/Kernel/Controller/EntityResourceTest.php
+++ b/modules/jsonapi/tests/src/Kernel/Controller/EntityResourceTest.php
@@ -166,7 +166,7 @@ class EntityResourceTest extends JsonapiKernelTestBase {
 
   /**
    * @covers ::getIndividual
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    */
   public function testGetIndividualDenied() {
     $role = Role::load(RoleInterface::ANONYMOUS_ID);
diff --git a/modules/jsonapi/tests/src/Unit/Access/CustomParameterNamesTest.php b/modules/jsonapi/tests/src/Unit/Access/CustomParameterNamesTest.php
index 632b402..7ba1845 100644
--- a/modules/jsonapi/tests/src/Unit/Access/CustomParameterNamesTest.php
+++ b/modules/jsonapi/tests/src/Unit/Access/CustomParameterNamesTest.php
@@ -72,7 +72,7 @@ class CustomParameterNamesTest extends \PHPUnit_Framework_TestCase {
       '>',
       '?',
       '@',
-      '“',
+      '\\',
       '^',
       '`',
       '{',
@@ -84,6 +84,10 @@ class CustomParameterNamesTest extends \PHPUnit_Framework_TestCase {
       $data['unsafe-' . $unsafe_char] = ['kitt' . $unsafe_char . 'ens', FALSE];
     }
 
+    for ($ascii = 0; $ascii <= 0x1F; $ascii++) {
+      $data['unsafe-' . $ascii] = ['kitt' . chr($ascii) . 'ens', FALSE];
+    }
+
     return $data;
   }
 
diff --git a/modules/jsonapi/tests/src/Unit/Context/FieldResolverTest.php b/modules/jsonapi/tests/src/Unit/Context/FieldResolverTest.php
index 12fa6b0..0fe7e6c 100644
--- a/modules/jsonapi/tests/src/Unit/Context/FieldResolverTest.php
+++ b/modules/jsonapi/tests/src/Unit/Context/FieldResolverTest.php
@@ -97,7 +97,7 @@ class FieldResolverTest extends UnitTestCase {
    *
    * @covers ::resolveInternal
    *
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    */
   public function testResolveInternalError() {
     $field_manager = $this->prophesize(EntityFieldManagerInterface::class);
diff --git a/modules/jsonapi/tests/src/Unit/LinkManager/LinkManagerTest.php b/modules/jsonapi/tests/src/Unit/LinkManager/LinkManagerTest.php
index 65ccefe..996e59c 100644
--- a/modules/jsonapi/tests/src/Unit/LinkManager/LinkManagerTest.php
+++ b/modules/jsonapi/tests/src/Unit/LinkManager/LinkManagerTest.php
@@ -120,7 +120,7 @@ class LinkManagerTest extends UnitTestCase {
    * Test errors.
    *
    * @covers ::getPagerLinks
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    * @dataProvider getPagerLinksErrorProvider
    */
   public function testGetPagerLinksError($offset, $size, $total, array $pages) {
diff --git a/modules/jsonapi/tests/src/Unit/Normalizer/EntityReferenceFieldNormalizerTest.php b/modules/jsonapi/tests/src/Unit/Normalizer/EntityReferenceFieldNormalizerTest.php
index 144ffc6..2f27c5d 100644
--- a/modules/jsonapi/tests/src/Unit/Normalizer/EntityReferenceFieldNormalizerTest.php
+++ b/modules/jsonapi/tests/src/Unit/Normalizer/EntityReferenceFieldNormalizerTest.php
@@ -130,7 +130,7 @@ class EntityReferenceFieldNormalizerTest extends UnitTestCase {
 
   /**
    * @covers ::denormalize
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    * @dataProvider denormalizeInvalidResourceProvider
    */
   public function testDenormalizeInvalidResource($data, $field_name) {
diff --git a/modules/jsonapi/tests/src/Unit/Routing/Param/FilterTest.php b/modules/jsonapi/tests/src/Unit/Routing/Param/FilterTest.php
index ebddb20..15b1928 100644
--- a/modules/jsonapi/tests/src/Unit/Routing/Param/FilterTest.php
+++ b/modules/jsonapi/tests/src/Unit/Routing/Param/FilterTest.php
@@ -87,7 +87,7 @@ class FilterTest extends UnitTestCase {
 
   /**
    * @covers ::get
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    */
   public function testGetFail() {
     $pager = new Filter(
diff --git a/modules/jsonapi/tests/src/Unit/Routing/Param/OffsetPageTest.php b/modules/jsonapi/tests/src/Unit/Routing/Param/OffsetPageTest.php
index a5fb407..c23e5e0 100644
--- a/modules/jsonapi/tests/src/Unit/Routing/Param/OffsetPageTest.php
+++ b/modules/jsonapi/tests/src/Unit/Routing/Param/OffsetPageTest.php
@@ -35,7 +35,7 @@ class OffsetPageTest extends UnitTestCase {
 
   /**
    * @covers ::get
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    */
   public function testGetFail() {
     $pager = new OffsetPage('lorem');
diff --git a/modules/jsonapi/tests/src/Unit/Routing/Param/SortTest.php b/modules/jsonapi/tests/src/Unit/Routing/Param/SortTest.php
index 5774029..a407ea5 100644
--- a/modules/jsonapi/tests/src/Unit/Routing/Param/SortTest.php
+++ b/modules/jsonapi/tests/src/Unit/Routing/Param/SortTest.php
@@ -52,7 +52,7 @@ class SortTest extends UnitTestCase {
   /**
    * @covers ::get
    * @dataProvider getFailProvider
-   * @expectedException \Drupal\jsonapi\Error\SerializableHttpException
+   * @expectedException \Drupal\jsonapi\Exception\SerializableHttpException
    */
   public function testGetFail($input) {
     $sort = new Sort($input);