validation.xml

<constraint-mapping xmlns="http://www.symfony-project.org/schema/dic/constraint-mapping"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.symfony-project.org/schema/dic/constraint-mapping
        http://www.symfony-project.org/schema/dic/services/constraint-mapping-1.0.xsd">

    <class name="Test\FileBundle\Entity\File">
        <property name="title">
            <constraint name="NotBlank">
                <option name="message">error.title.empty</option>
            </constraint>
        </property>