Block Hooks: Return early from saving meta data for the navigation without a $post->ID

packages/block-library/src/navigation/index.php

@@ -1512,6 +1512,14 @@ function block_core_navigation_set_ignored_hooked_blocks_metadata( $inner_blocks
  * @return stdClass The updated post object.
  */
 function block_core_navigation_update_ignore_hooked_blocks_meta( $post ) {
+	/*
+	 * In this scenario the user has likely tried to create a navigation via the REST API.
+	 * In which case we won't have a post ID to work with and store meta against.
+	 */
+	if ( empty( $post->ID ) ) {
+		return $post;
+	}
+
 	/*
 	 * We run the Block Hooks mechanism to inject the `metadata.ignoredHookedBlocks` attribute into
 	 * all anchor blocks. For the root level, we create a mock Navigation and extract them from there.

phpunit/blocks/block-navigation-block-hooks-test.php

@@ -59,7 +59,7 @@ public function tear_down() {
 	 */
 	public function test_block_core_navigation_update_ignore_hooked_blocks_meta_preserves_entities() {
 		if ( ! function_exists( 'set_ignored_hooked_blocks_metadata' ) ) {
-			$this->markTestSkipped( 'Test skipped on WordPress versions that do not included required Block Hooks functionalit.' );
+			$this->markTestSkipped( 'Test skipped on WordPress versions that do not included required Block Hooks functionality.' );
 		}
 
 		register_block_type(
@@ -92,4 +92,34 @@ public function test_block_core_navigation_update_ignore_hooked_blocks_meta_pres
 			'Block was not added to ignored hooked blocks metadata.'
 		);
 	}
+
+	/**
+	 * @covers ::gutenberg_block_core_navigation_update_ignore_hooked_blocks_meta
+	 */
+	public function test_block_core_navigation_dont_modify_no_post_id() {
+		if ( ! function_exists( 'set_ignored_hooked_blocks_metadata' ) ) {
+			$this->markTestSkipped( 'Test skipped on WordPress versions that do not included required Block Hooks functionality.' );
+		}
+
+		register_block_type(
+			'tests/my-block',
+			array(
+				'block_hooks' => array(
+					'core/navigation' => 'last_child',
+				),
+			)
+		);
+
+		$original_markup    = '<!-- wp:navigation-link {"label":"News","type":"page","id":2,"url":"http://localhost:8888/?page_id=2","kind":"post-type"} /-->';
+		$post               = new stdClass();
+		$post->post_content = $original_markup;
+
+		$post = gutenberg_block_core_navigation_update_ignore_hooked_blocks_meta( $post );
+
+		$this->assertSame(
+			$original_markup,
+			$post->post_content,
+			'Post content did not match the original markup.'
+		);
+	}
 }