Index: DBAL/Types/DecimalType.php
===================================================================
--- DBAL/Types/DecimalType.php	(revision 2)
+++ DBAL/Types/DecimalType.php	(working copy)
@@ -42,6 +42,6 @@
 
     public function convertToPHPValue($value, AbstractPlatform $platform)
     {
-        return (double) $value;
+        return null === $value ? null : (double) $value;
     }
 }
\ No newline at end of file
Index: DBAL/Types/SmallIntType.php
===================================================================
--- DBAL/Types/SmallIntType.php	(revision 2)
+++ DBAL/Types/SmallIntType.php	(working copy)
@@ -42,7 +42,7 @@
 
     public function convertToPHPValue($value, AbstractPlatform $platform)
     {
-        return (int) $value;
+        return null === $value ? null : (int) $value;
     }
 
     public function getBindingType()