diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
index 6ff9e10..0737733 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
@@ -165,16 +165,21 @@ public function setValue($values, $notify = TRUE) {
       if (isset($values['target_id']) && !isset($values['entity'])) {
         $this->onChange('target_id', FALSE);
       }
-      elseif (!isset($values['target_id']) && isset($values['entity'])) {
+      // NULL is a valid value, so we use array_key_exists().
+      elseif (is_array($values) && !array_key_exists('target_id', $values) && isset($values['entity'])) {
         $this->onChange('entity', FALSE);
       }
-      elseif (isset($values['target_id']) && isset($values['entity'])) {
+      // NULL is a valid value, so we use array_key_exists().
+      elseif (is_array($values) && array_key_exists('target_id', $values) && isset($values['entity'])) {
         // If both properties are passed, verify the passed values match. The
         // only exception we allow is when we have a new entity: in this case
         // its actual id and target_id will be different, due to the new entity
         // marker.
         $entity_id = $this->get('entity')->getTargetIdentifier();
-        if ($entity_id != $values['target_id'] && (!$this->entity->isNew())) {
+        // If the entity has been saved and we're trying to set both the
+        // target_id and the entity values with a non-null target ID, then the
+        // value for target_id should match the ID of the entity value.
+        if (!$this->entity->isNew() && $values['target_id'] !== NULL && ($entity_id !== $values['target_id'])) {
           throw new \InvalidArgumentException('The target id and entity passed to the entity reference item do not match.');
         }
       }
@@ -210,7 +215,7 @@ public function onChange($property_name, $notify = TRUE) {
       $target_id = $property->isTargetNew() ? NULL : $property->getTargetIdentifier();
       $this->writePropertyValue('target_id', $target_id);
     }
-    elseif ($property_name == 'target_id' && $this->target_id) {
+    elseif ($property_name == 'target_id' && $this->target_id !== NULL) {
       $this->writePropertyValue('entity', $this->target_id);
     }
     parent::onChange($property_name, $notify);
@@ -236,11 +241,12 @@ public function preSave() {
       if ($this->entity->isNew()) {
         $this->entity->save();
       }
-    }
-    if ($this->entity && ($id = $this->entity->id()) && $this->target_id !== $id) {
       // Make sure the parent knows we are updating this property so it can
       // react properly.
-      $this->target_id = $id;
+      $this->target_id = $this->entity->id();
+    }
+    if (!$this->isEmpty() && $this->target_id === NULL) {
+      $this->target_id = $this->entity->id();
     }
   }
 
diff --git a/core/modules/system/src/Tests/Entity/EntityReferenceFieldTest.php b/core/modules/system/src/Tests/Entity/EntityReferenceFieldTest.php
index 14a67ef..01dd0c1 100644
--- a/core/modules/system/src/Tests/Entity/EntityReferenceFieldTest.php
+++ b/core/modules/system/src/Tests/Entity/EntityReferenceFieldTest.php
@@ -238,16 +238,16 @@ function testAutocreateApi() {
     });
     $this->assertUserAutocreate($entity, function(EntityInterface $entity, UserInterface $user) {
       $entity->user_id[0]->get('entity')->setValue($user);
-      $entity->user_id[0]->get('target_id')->setValue(-1);
+      $entity->user_id[0]->get('target_id')->setValue(NULL);
     });
     $this->assertUserAutocreate($entity, function(EntityInterface $entity, UserInterface $user) {
-      $entity->user_id->setValue(array('entity' => $user, 'target_id' => -1));
+      $entity->user_id->setValue(array('entity' => $user, 'target_id' => NULL));
     });
     try {
       $message = 'Setting both the entity and an invalid target_id property fails.';
       $this->assertUserAutocreate($entity, function(EntityInterface $entity, UserInterface $user) {
         $user->save();
-        $entity->user_id->setValue(array('entity' => $user, 'target_id' => -1));
+        $entity->user_id->setValue(array('entity' => $user, 'target_id' => $this->generateRandomEntityId()));
       });
       $this->fail($message);
     }
@@ -273,16 +273,16 @@ function testAutocreateApi() {
     });
     $this->assertUserRoleAutocreate($entity, function(EntityInterface $entity, RoleInterface $role) {
       $entity->user_role[0]->get('entity')->setValue($role);
-      $entity->user_role[0]->get('target_id')->setValue(-1);
+      $entity->user_role[0]->get('target_id')->setValue(NULL);
     });
     $this->assertUserRoleAutocreate($entity, function(EntityInterface $entity, RoleInterface $role) {
-      $entity->user_role->setValue(array('entity' => $role, 'target_id' => -1));
+      $entity->user_role->setValue(array('entity' => $role, 'target_id' => NULL));
     });
     try {
       $message = 'Setting both the entity and an invalid target_id property fails.';
       $this->assertUserRoleAutocreate($entity, function(EntityInterface $entity, RoleInterface $role) {
         $role->save();
-        $entity->user_role->setValue(array('entity' => $role, 'target_id' => -1));
+        $entity->user_role->setValue(array('entity' => $role, 'target_id' => $this->generateRandomEntityId(TRUE)));
       });
       $this->fail($message);
     }