zf2 + Doctrine2 Integrity constraint violation: 1048 Column '' cannot be null - doctrine-orm

Question

I have a problem with Doctrine2 it throws me this exception:
An exception occurred while executing 'INSERT INTO sesion (Contrasena, Estado, UsuarioIdentificacion) VALUES (?, ?, ?)' with params ["j15474874654j", "1", null]:
SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'UsuarioIdentificacion' cannot be null
I am a beginner with doctrine 2 and I could not resolve this error, I think the error is in relationships. I've read other similar problems, but I have not succeeded.
I would greatly appreciate the help. this is my code:
In my controller:
$usuario = new Usuario();
$data = $request->getPost();
$usuario->setNombre($data['nombre']);
$usuario->setApellidos($data['apellidos']);
$usuario->setIdentificacion($data['identificacion']);
$usuario->setTitulo($data['titulo']);
$usuario->setContacto($data['contacto']);
$usuario->setCorreo($data['correo'] . "#correounivalle.edu.co");
$sesion = new Sesion();
$sesion->setUsuarioidentificacion($usuario);
$sesion->setEstado("1");
$sesion->setContrasena($data['nombre'][0].$data['identificacion'].$data['apellidos'][0]);
$em->persist($usuario);
$em->persist($sesion);
$em->flush();
class usuario:
<?php
namespace DBAL\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* Usuario
*
* #ORM\Table(name="usuario", uniqueConstraints={#ORM\UniqueConstraint(name="Identificacion", columns={"Identificacion"}), #ORM\UniqueConstraint(name="Correo", columns={"Correo"})})
* #ORM\Entity
* #ORM\Entity(repositoryClass="DBAL\Repository\UsuarioRepository")
*/
class Usuario
{
/**
* #var integer
*
* #ORM\Column(name="Id", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="IDENTITY")
*/
private $id;
/**
* #var integer
*
* #ORM\Column(name="Identificacion", type="integer", nullable=false)
*/
private $identificacion;
/**
* #var string
*
* #ORM\Column(name="Nombre", type="string", length=50, nullable=false)
*/
private $nombre;
/**
* #var string
*
* #ORM\Column(name="Apellidos", type="string", length=50, nullable=false)
*/
private $apellidos;
/**
* #var string
*
* #ORM\Column(name="Correo", type="string", length=100, nullable=false)
*/
private $correo;
/**
* #var integer
*
* #ORM\Column(name="Contacto", type="integer", nullable=true)
*/
private $contacto;
/**
* #var string
*
* #ORM\Column(name="Titulo", type="string", length=20, nullable=true)
*/
private $titulo;
/*with their respective setter and getter*/
class sesion:
<?php
namespace DBAL\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* Sesion
*
* #ORM\Table(name="sesion", indexes={#ORM\Index(name="UsuarioIdentificacion", columns={"UsuarioIdentificacion"}), #ORM\Index(name="sesion", columns={"UsuarioIdentificacion"})})
* #ORM\Entity
*/
class Sesion
{
/**
* #var integer
*
* #ORM\Column(name="Id", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="IDENTITY")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="Contrasena", type="string", length=50, nullable=false)
*/
private $contrasena;
/**
* #var boolean
*
* #ORM\Column(name="Estado", type="boolean", nullable=false)
*/
private $estado;
/**
* #var \Usuario
*
*
* #ORM\OneToOne(targetEntity="Usuario")
* #ORM\JoinColumns({
* #ORM\JoinColumn(name="UsuarioIdentificacion", referencedColumnName="Correo")
* })
*/
private $usuarioidentificacion;
/**
* #var \Doctrine\Common\Collections\Collection
*
* #ORM\ManyToMany(targetEntity="Roles", mappedBy="sesionusuarioidentificacion")
*/
private $rolesid;
/**
* Constructor
*/
public function __construct()
{
$this->rolesid = new \Doctrine\Common\Collections\ArrayCollection();
}
/**
* Get id
*
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* Set contrasena
*
* #param string $contrasena
*
* #return Sesion
*/
public function setContrasena($contrasena)
{
$this->contrasena = $contrasena;
return $this;
}
/**
* Get contrasena
*
* #return string
*/
public function getContrasena()
{
return $this->contrasena;
}
/**
* Set estado
*
* #param boolean $estado
*
* #return Sesion
*/
public function setEstado($estado)
{
$this->estado = $estado;
return $this;
}
/**
* Get estado
*
* #return boolean
*/
public function getEstado()
{
return $this->estado;
}
/**
* Set usuarioidentificacion
*
* #param \DBAL\Entity\Usuario $usuarioidentificacion
*
* #return Sesion
*/
public function setUsuarioidentificacion(\DBAL\Entity\Usuario $usuarioidentificacion)
{
$this->usuarioidentificacion = $usuarioidentificacion;
return $this;
}
/**
* Get usuarioidentificacion
*
* #return \Usuario
*/
public function getUsuarioidentificacion()
{
return $this->usuarioidentificacion;
}
/**
* Add rolesid
*
* #param \Roles $rolesid
*
* #return Sesion
*/
public function addRolesid(\Roles $rolesid)
{
$this->rolesid[] = $rolesid;
return $this;
}
/**
* Remove rolesid
*
* #param \Roles $rolesid
*/
public function removeRolesid(\Roles $rolesid)
{
$this->rolesid->removeElement($rolesid);
}
/**
* Get rolesid
*
* #return \Doctrine\Common\Collections\Collection
*/
public function getRolesid()
{
return $this->rolesid;
}
If someone could help me, I really need it and I have already searched a lot and attempted in many ways, but really not fix it.