diff --git a/src/Row.php b/src/Row.php
index b204795..58fbd7a 100644
--- a/src/Row.php
+++ b/src/Row.php
@@ -69,7 +69,7 @@ public function __set($name, $value)
      */
     public function __isset($name)
     {
-        return !empty($this->values[$name]);
+        return !empty($this->values[$name]) && !($this->values[$name] instanceof NullValue);
     }
 
     /**