diff -up ./src/Framework/MockObject/Generator.php.old ./src/Framework/MockObject/Generator.php
--- ./src/Framework/MockObject/Generator.php.old	2021-03-18 14:27:57.237056358 +0100
+++ ./src/Framework/MockObject/Generator.php	2021-03-18 14:28:03.916026672 +0100
@@ -1207,13 +1207,13 @@ class PHPUnit_Framework_MockObject_Gener
                     }
 
                     $typeDeclaration = $typename . ' ';
-                } elseif ($parameter->isArray()) {
+                } elseif (@$parameter->isArray()) {
                     $typeDeclaration = 'array ';
-                } elseif ($parameter->isCallable()) {
+                } elseif (@$parameter->isCallable()) {
                     $typeDeclaration = 'callable ';
                 } else {
                     try {
-                        $class = $parameter->getClass();
+                        $class = @$parameter->getClass();
                     } catch (ReflectionException $e) {
                         throw new PHPUnit_Framework_MockObject_RuntimeException(
                             sprintf(