Avoid exception when superclass is null and no docblock is provided for a method

src/Converter.php

@@ -284,7 +284,7 @@ private function getDocBlock(Project $project, int $objectType, string $namespac
                         }
 
                         $parentFqsen = $obj->getParent();
-                        if (!$parent = $this->getObject($project, $parentFqsen, self::OBJECT_CLASS)) {
+                        if (null === $parentFqsen || !$parent = $this->getObject($project, $parentFqsen, self::OBJECT_CLASS)) {
                             return;
                         }
 

tests/Fixtures/Foo.php

@@ -7,6 +7,10 @@
  */
 class Foo
 {
+    public function bar($foo)
+    {
+    }
+
     /**
      * @param float $a
      */

tests/test.php

@@ -120,6 +120,10 @@ function test(string $a = null)
  */
 class Foo
 {
+    public function bar($foo)
+    {
+    }
+
     /**
      * @param float $a
      */