diff --git a/Form/Type/CenterType.php b/Form/Type/CenterType.php
index e226c77ca..41db8dc98 100644
--- a/Form/Type/CenterType.php
+++ b/Form/Type/CenterType.php
@@ -25,6 +25,8 @@ use Symfony\Component\Form\FormBuilderInterface;
 use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorage;
 use Chill\MainBundle\Entity\Center;
 use Chill\MainBundle\Form\Type\DataTransformer\CenterTransformer;
+use Symfony\Component\Form\Extension\Core\Type\HiddenType;
+use Symfony\Bridge\Doctrine\Form\Type\EntityType;
 
 /**
  *
@@ -78,9 +80,9 @@ class CenterType extends AbstractType
             throw new \RuntimeException("The user is not associated with "
                     . "any center. Associate user with a center");
         } elseif ($nbReachableCenters === 1) {
-            return 'hidden';
+            return HiddenType::class;
         } else {
-            return 'entity';
+            return EntityType::class;
         }
     }
 
@@ -93,7 +95,8 @@ class CenterType extends AbstractType
     public function configureOptions(OptionsResolver $resolver)
     {
         if (count($this->reachableCenters) > 1) {
-            $resolver->setDefault('class', 'Chill\MainBundle\Entity\Center');
+            $resolver->setDefault('class', Center::class);
+            $resolver->setDefault('choices', $this->reachableCenters);
         }
     }
 
@@ -105,7 +108,7 @@ class CenterType extends AbstractType
      */
     public function buildForm(FormBuilderInterface $builder, array $options)
     {
-        if ($this->getParent() === 'hidden') {
+        if ($this->getParent() === HiddenType::class) {
             $builder->addModelTransformer($this->transformer);
         }
     }
diff --git a/Test/Export/AbstractAggregatorTest.php b/Test/Export/AbstractAggregatorTest.php
index a1f0cf60a..d33a6f88d 100644
--- a/Test/Export/AbstractAggregatorTest.php
+++ b/Test/Export/AbstractAggregatorTest.php
@@ -213,7 +213,7 @@ abstract class AbstractAggregatorTest extends KernelTestCase
         $nbOfFrom   = $query->getDQLPart('from') !== null ? 
             count($query->getDQLPart('from')) : 0;
         $nbOfWhere  = $query->getDQLPart('where') !== null ? 
-            count($query->getDQLPart('where')) : 0;
+            $query->getDQLPart('where')->count() : 0;
         $nbOfSelect = $query->getDQLPart('select') !== null ?
             count($query->getDQLPart('select')) : 0;
         
@@ -226,7 +226,7 @@ abstract class AbstractAggregatorTest extends KernelTestCase
                 altered the query");
         $this->assertGreaterThanOrEqual(
             $nbOfWhere, 
-            $query->getDQLPart('where') !== null ? count($query->getDQLPart('where')) : 0,
+            $query->getDQLPart('where') !== null ? $query->getDQLPart('where')->count() : 0,
             "Test that there are equal or more 'where' clause after that the filter has"
             . "altered the query");
         $this->assertGreaterThanOrEqual(
diff --git a/Test/Export/AbstractFilterTest.php b/Test/Export/AbstractFilterTest.php
index c16bfb8c0..7721b9212 100644
--- a/Test/Export/AbstractFilterTest.php
+++ b/Test/Export/AbstractFilterTest.php
@@ -104,20 +104,32 @@ abstract class AbstractFilterTest extends KernelTestCase
     public function testAlterQuery(QueryBuilder $query, $data)
     {
         // retains informations about query
-        $nbOfFrom = count($query->getDQLPart('from'));
-        $nbOfWhere = count($query->getDQLPart('where'));
-        $nbOfSelect = count($query->getDQLPart('select'));
+        $nbOfFrom   = $query->getDQLPart('from') !== null ? 
+            count($query->getDQLPart('from')) : 0;
+        $nbOfWhere  = $query->getDQLPart('where') !== null ? 
+            $query->getDQLPart('where')->count() : 0;
+        $nbOfSelect = $query->getDQLPart('select') !== null ?
+            count($query->getDQLPart('select')) : 0;
         
         $this->getFilter()->alterQuery($query, $data);
         
-        $this->assertGreaterThanOrEqual($nbOfFrom, count($query->getDQLPart('from')),
+        $this->assertGreaterThanOrEqual(
+            $nbOfFrom, 
+            $query->getDQLPart('from') !== null ? count($query->getDQLPart('from')) : 0,
             "Test that there are equal or more 'from' clause after that the filter has 
-                altered the query");
-        $this->assertGreaterThanOrEqual($nbOfWhere, count($query->getDQLPart('where')),
+                altered the query"
+            );
+        $this->assertGreaterThanOrEqual(
+            $nbOfWhere, 
+            $query->getDQLPart('where') !== null ? $query->getDQLPart('where')->count() : 0,
             "Test that there are equal or more 'where' clause after that the filter has"
-            . "altered the query");
-        $this->assertEquals($nbOfSelect, count($query->getDQLPart('select')),
-            "Test that the filter has no altered the 'select' part of the query");
+            . "altered the query"
+            );
+        $this->assertEquals(
+            $nbOfSelect, 
+            $query->getDQLPart('select') !== null ? count($query->getDQLPart('select')) : 0,
+            "Test that the filter has no altered the 'select' part of the query"
+            );
         
     }
     
diff --git a/Tests/Form/Type/CenterTypeTest.php b/Tests/Form/Type/CenterTypeTest.php
index 8c3d2f290..48b96375e 100644
--- a/Tests/Form/Type/CenterTypeTest.php
+++ b/Tests/Form/Type/CenterTypeTest.php
@@ -23,6 +23,8 @@ use Symfony\Component\Form\Test\TypeTestCase;
 use Chill\MainBundle\Form\Type\CenterType;
 use Chill\MainBundle\Entity\User;
 use Chill\MainBundle\Entity\GroupCenter;
+use Symfony\Component\Form\Extension\Core\Type\HiddenType;
+use Symfony\Bridge\Doctrine\Form\Type\EntityType;
 
 
 /**
@@ -48,7 +50,7 @@ class CenterTypeTest extends TypeTestCase
         
         $type = $this->prepareType($user);
       
-        $this->assertEquals('hidden', $type->getParent());
+        $this->assertEquals(HiddenType::class, $type->getParent());
     }
     
     /**
@@ -71,7 +73,7 @@ class CenterTypeTest extends TypeTestCase
         
         $type = $this->prepareType($user);
       
-        $this->assertEquals('hidden', $type->getParent());
+        $this->assertEquals(HiddenType::class, $type->getParent());
     }
     
     /**
@@ -96,7 +98,7 @@ class CenterTypeTest extends TypeTestCase
         
         $type = $this->prepareType($user);
         
-        $this->assertEquals('entity', $type->getParent());
+        $this->assertEquals(EntityType::class, $type->getParent());
     }
     
     /**