Check if variable array key exists before execution method (#2182)

* Check if variable array key exists before execution method

* fix formatting

* use array function for check

* attempt to fix style issue

---------

Co-authored-by: Vlado Hudak <vlado@grownapps.io>

OpenApiPhp/Util.php

@@ -424,7 +424,7 @@ private static function mergeFromArray(OA\AbstractAnnotation $annotation, array
             if ('$ref' === $propertyName) {
                 $propertyName = 'ref';
             }
-            if (!\in_array($propertyName, $done, true)) {
+            if (array_key_exists($propertyName, $defaults) && !\in_array($propertyName, $done, true)) {
                 self::mergeProperty($annotation, $propertyName, $value, $defaults[$propertyName], $overwrite);
             }
         }