Handle empty documents slightly better

Previously, we’d crash because the documentElement is null in this case.

Author: lucaswerkmeister

src/Component.php

@@ -95,6 +95,10 @@ private function parseHtml( $html ) {
 	 * @throws Exception
 	 */
 	private function getRootNode( DOMDocument $document ) {
+		if ( $document->documentElement === null ) {
+			throw new Exception( 'Empty document' );
+		}
+
 		$rootNodes = $document->documentElement->childNodes->item( 0 )->childNodes;
 
 		if ( $rootNodes->length > 1 ) {

tests/php/TemplatingTest.php

@@ -17,6 +17,11 @@ public function testJustASingleEmptyHtmlElement() {
 		$this->assertSame( '<div></div>', $result );
 	}
 
+	public function testTemplateHasNoRootNodes_ThrowsAnException(): void {
+		$this->expectException( Exception::class );
+		$this->createAndRender( '', [] );
+	}
+
 	public function testTemplateHasTwoRootNodes_ThrowsAnException() {
 		$this->expectException( Exception::class );
 		$this->createAndRender( '<p></p><p></p>', [] );