do not check sandbox for __toString if method does not exist on object

src/Extension/SandboxExtension.php

@@ -93,7 +93,7 @@ class SandboxExtension extends AbstractExtension
 
     public function ensureToStringAllowed($obj)
     {
-        if ($this->isSandboxed() && \is_object($obj)) {
+        if ($this->isSandboxed() && \is_object($obj) && method_exists($obj, '__toString')) {
             $this->policy->checkMethodAllowed($obj, '__toString');
         }
 

test/Twig/Tests/Node/SandboxedPrintTest.php

@@ -9,12 +9,9 @@
  * file that was distributed with this source code.
  */
 
-use Twig\Node\Expression\ArrayExpression;
 use Twig\Node\Expression\ConstantExpression;
-use Twig\Node\Expression\GetAttrExpression;
 use Twig\Node\Expression\NameExpression;
 use Twig\Node\SandboxedPrintNode;
-use Twig\Template;
 use Twig\Test\NodeTestCase;
 
 class Twig_Tests_Node_SandboxedPrintTest extends NodeTestCase