input filter no object exists

inputfilteR_noobject.php

            $inputFilter->add(
                    $factory->createInput(array(
                            'name'    => 'email',
                            'required' => true,
                            'filters' => array(
                                    array('name' => 'StripTags'),
                                    array('name' => 'StringTrim')
                            ),
                            'validators' => array(
                                    array(
                                            'name'    => 'EmailAddress'
                                    ),
                                    array(
                                            'name'        => 'StringLength',
                                            'options'   => array(
                                                    'encoding'    => 'UTF-8',
                                                    'min'        => 1,
                                                    'max'        => 150
                                            )
                                    ),
                                    array(
                                            'name'     => 'DoctrineModule\Validator\NoObjectExists',
                                            'options'  => array(
                                                    'object_repository' => $this->entityManager->getRepository('Admin\Entity\User'),
                                                    'fields'            => array('email')
                                            )
                                    )
                            )
                    ))
            );