diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index e3cb3e6..775ecc2 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -233,6 +233,7 @@ class Configuration
                     ->scalarNode('index')->end()
                     ->scalarNode('analyzer')->end()
                     ->scalarNode('term_vector')->end()
+                    ->scalarNode('null_value')->end()
                     ->arrayNode('fields')
                         ->useAttributeAsKey('name')
                         ->prototype('array')
@@ -245,6 +246,7 @@ class Configuration
                                 ->scalarNode('index')->end()
                                 ->scalarNode('analyzer')->end()
                                 ->scalarNode('term_vector')->end()
+                                ->scalarNode('null_value')->end()
                             ->end()
                         ->end()
                     ->end()