assertNulL example

$this->assertEquals(CommentItemInterface::OPEN, $translation->comment_node_article->status);
    $this->assertEquals('Home', $translation->field_link->title);
    $term_ref = $translation->get('field_vocab_localize')->target_id;
    $this->assertSame('20', $term_ref);
    $this->assertSame('DS9', Term::load($term_ref)->getName());

    $term_ref = $translation->get('field_vocab_translate')->target_id;
    $this->assertSame('23', $term_ref);
    $this->assertSame('is - High council', Term::load($term_ref)->getName());

    $term_ref = $translation->get('field_vocab_fixed')->target_id;
    $this->assertNulL($term_ref);

    // Test that content_translation_source is set.     $manager = $this->container->get('content_translation.manager');
    $this->assertEquals('en', $manager->getTranslationMetadata($node->getTranslation('is'))->getSource());

    // Node 3 is a translation of node 2, and should not be imported separately.     $this->assertNull(Node::load(3), "Node 3 doesn't exist in D8, it was a translation");

    // Test that content_translation_source for a source other than English.     $node = Node::load(4);
    $this->assertEquals('is', $manager->getTranslationMetadata($node->getTranslation('en'))->getSource());