ACP2E-3660: REST endpoint Product Import Json not validate the mandatory fields

Author: aplapana

app/code/Magento/CatalogImportExport/Model/Import/Product/Validator.php

@@ -458,6 +458,7 @@ public function isValid($value)
                 //prioritize specialized validation
                 if ($validator->getFieldName() &&
                     isset($validatedAttributes['attributes']) &&
+                    isset($validatedAttributes['attributes'][$validator->getFieldName()]) &&
                     $validatedAttributes['attributes'][$validator->getFieldName()] === false
                 ) {
                     $validatedAttributes['attributes'][$validator->getFieldName()] = true;