diff --git a/src/Mapper.php b/src/Mapper.php
index 00395fe..737efeb 100644
--- a/src/Mapper.php
+++ b/src/Mapper.php
@@ -410,9 +410,7 @@ public function mapToSalesforceObject($model)
         $allMappings = $mappedProperties->toArray() + $mappedRelations;
 
         foreach ($allMappings as $property => $mapping) {
-            if(isset($value)) {
-                unset($value);
-            }
+            $value = null;
             if ($mapping instanceof Annotation\Field) {
                 $fieldDescription = $objectDescription->getField($mapping->name);
                 $fieldName = $mapping->name;