Fix index wide finder config check

Fixes index wide finder configuration. Fixes #61

DependencyInjection/Configuration.php

@@ -71,7 +71,10 @@ class Configuration
                         ->performNoDeepMerging()
                         ->children()
                             ->scalarNode('client')->end()
-                            ->scalarNode('finder')->end()
+                            ->scalarNode('finder')
+                                ->treatNullLike(true)
+                                ->defaultFalse()
+                            ->end()
                             ->arrayNode('type_prototype')
                                 ->children()
                                     ->arrayNode('persistence')

DependencyInjection/FOQElasticaExtension.php

@@ -113,7 +113,7 @@ class FOQElasticaExtension extends Extension
                     'mappings' => array()
                 )
             );
-            if (isset($index['finder'])) {
+            if ($index['finder']) {
                 $this->loadIndexFinder($container, $name, $indexId);
             }
             if (!empty($index['settings'])) {