get entity type id from the proper place

modules/salesforce_mapping/src/MappedObjectStorage.php

@@ -53,7 +53,6 @@ class MappedObjectStorage extends ConfigEntityStorage {
    * {@inheritdoc}
    */
   public function __construct($entity_type_id, ConfigFactoryInterface $config_factory, UuidInterface $uuid_service, LanguageManagerInterface $language_manager, EntityManagerInterface $entity_manager) {
-    $this->entity_type_id = $entity_type_id;
     $entity_type = $entity_manager->getDefinition($entity_type_id);
     parent::__construct($entity_type, $config_factory, $uuid_service, $language_manager);
   }

modules/salesforce_mapping/src/SalesforceMappingStorage.php

@@ -49,13 +49,10 @@ class MappedObjectStorage extends SqlContentEntityStorage {
    */
   protected $entityManager;
 
-  private $entity_type_id;
-
   /**
    * {@inheritdoc}
    */
   public function __construct($entity_type_id, ConfigFactoryInterface $config_factory, UuidInterface $uuid_service, LanguageManagerInterface $language_manager, EntityManagerInterface $entity_manager) {
-    $this->entity_type_id = $entity_type_id;
     $entity_type = $entity_manager->getDefinition($entity_type_id);
     parent::__construct($entity_type, $config_factory, $uuid_service, $language_manager);
   }

modules/salesforce_mapping/src/ThrowsOnLoadTrait.php

@@ -4,10 +4,11 @@ namespace Drupal\salesforce_mapping;
 
 use Drupal\salesforce\EntityNotFoundException;
 
+/**
+ * This trait should be attached to an instance of EntityStorageInterface
+ */
 trait ThrowsOnLoadTrait {
 
-  protected $entity_type_id;
-
   /**
    * Returns entities for given ids or throws exception.
    *
@@ -25,7 +26,7 @@ trait ThrowsOnLoadTrait {
   public function loadMultiple(array $ids = NULL) {
     $entities = parent::loadMultiple($values);
     if (empty($mappings)) {
-      throw new EntityNotFoundException($properties, $this->entity_type_id);
+      throw new EntityNotFoundException($properties, $this->getEntityTypeId());
     }
     return $mappings;
   }
@@ -47,7 +48,7 @@ trait ThrowsOnLoadTrait {
   public function loadByProperties(array $properties = []) {
     $entities = parent::loadByProperties($properties);
     if (empty($mappings)) {
-      throw new EntityNotFoundException($properties, $this->entity_type_id);
+      throw new EntityNotFoundException($properties, $this->getEntityTypeId());
     }
     return $entities;    
   }