Update validation tests

- assert non-null ASTs
- additional submodules

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "validation/frameworks/drupal"]
 	path = validation/frameworks/drupal
 	url = https://github.com/drupal/drupal
+[submodule "validation/frameworks/tolerant-php-parser"]
+	path = validation/frameworks/tolerant-php-parser
+	url = https://github.com/microsoft/tolerant-php-parser

src/PhpDocument.php

@@ -229,9 +229,9 @@ class PhpDocument
     /**
      * Returns the AST of the document
      *
-     * @return Node[]
+     * @return Node[] | Tolerant\Node | null
      */
-    public function getStmts(): array
+    public function getStmts()
     {
         return $this->stmts;
     }

tests/Validation/ValidationTest.php

@@ -69,6 +69,8 @@ class ValidationTest extends TestCase
             $this->fail((string)$e);
         }
 
+        $this->assertNotNull($document->getStmts());
+
         if (file_exists($outFile)) {
             unlink($outFile);
         }