502 bad gateway при использовании связи @OneToMany Doctrine 2

Есть две сущности:

<?php
/**
 * Created by PhpStorm.
 * User: leonid.groshev
 * Date: 21.12.2016
 * Time: 12:31
 */
namespace Atelie\Entity;
use DateTime;
use Doctrine\Common\Collections\ArrayCollection;
use Symfony\Component\Serializer\Normalizer\NormalizableInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
/**
 * Class ShoesProduct
 *
 * @package Atelie\Entity
 *
 * @Entity(repositoryClass="Atelie\Doctrine\Repository\ShoesProductRepository") @Table(name="shoes_products")
 * @HasLifecycleCallbacks
 */
class ShoesProduct implements NormalizableInterface
{
    /**
     * @var int
     * @Id @Column(type="integer") @GeneratedValue
     */
    protected $id;
    /**
     * @var string
     * @Column(type="string")
     */
    protected $title = '';
    /**
     * @var string
     * @Column(type="text")
     */
    protected $description = '';
    /**
     * @var string
     * @Column(type="decimal", nullable = true, scale=2)
     */
    protected $price = '';
    /**
     * @var string
     * @Column(type="integer")
     */
    protected $difficulty = '';
    /**
     * @var bool
     * @Column(type="boolean", options={"default": true})
     */
    protected $new = true;
    /**
     * @var bool
     * @Column(type="boolean", options={"default": false})
     */
    protected $sale = false;
    /**
     * @var bool
     * @Column(type="boolean", options={"default": false})
     */
    protected $hot = false;
    /**
     * @var bool
     * @Column(type="boolean", options={"default": false})
     */
    protected $recommended = false;
    /**
     * @var string
     * @Column(type="integer", options={"default": 0})
     */
    protected $likes = 0;
    /**
     * @var DateTime
     * @Column(type="datetime")
     */
    protected $created_at;
    /**
     * @var DateTime
     * @Column(type="datetime", nullable = true)
     */
    protected $updated_at;
    /**
     * @var bool
     * @Column(type="boolean", options={"default": false})
     */
    protected $deleted = false;
    /**
     * Relations
     */
    /**
     * @var Document[]|ArrayCollection
     * @ManyToMany(targetEntity="Document")
     */
    protected $documents;
    /**
     * @var Textile
     * @ManyToOne(targetEntity="Textile")
     */
    protected $textile;
    /**
     * @var Purpose
     * @ManyToOne(targetEntity="Purpose")
     */
    protected $purpose;
    /**
     * @var Gender
     * @ManyToOne(targetEntity="Gender")
     */
    protected $gender;
    /**
     * @var Season
     * @ManyToOne(targetEntity="Season")
     */
    protected $season;
    /**
     * @var Type
     * @ManyToOne(targetEntity="Type")
     */
    protected $type;
    /**
     * @var Category
     * @ManyToOne(targetEntity="Category")
     */
    protected $category;
    /**
     * @var Brand
     * @ManyToOne(targetEntity="Brand")
     */
    protected $brand;
    /**
     * One Country has Many Regions.
     * @OneToMany(targetEntity="ShoesModel", mappedBy="shoes_product")
     */
    protected $shoes_models;
    function __construct()
    {
        $this->documents = new ArrayCollection();
        $this->shoes_models = new ArrayCollection();
    }
    /**
     * @return ShoesModel[]|ArrayCollection
     */
    public function getShoesModels()
    {
        return $this->shoes_models;
    }
    /**
     * @param ShoesModel[] $shoes_models
     * @return $this
     */
    public function setShoesModels($shoes_models)
    {
        $this->shoes_models = $shoes_models;
        return $this;
    }
    /**
     * @return int
     */
    public function getId()
    {
        return $this->id;
    }
    /**
     * Create and Update time
     * @PrePersist
     * @PreUpdate
     */
    public function updatedTimestamps()
    {
        if ($this->created_at == null) {
            $this->created_at = new DateTime('now');
        }
        else {
            $this->updated_at = new DateTime('now');
        }
    }
    /**
     * @return DateTime
     */
    public function getCreatedAt()
    {
        return $this->created_at;
    }
    /**
     * @return DateTime
     */
    public function getUpdatedAt()
    {
        return $this->updated_at;
    }
    /**
     * @return string
     */
    public function getTitle()
    {
        return $this->title;
    }
    /**
     * @param string $title
     * @return $this
     */
    public function setTitle($title)
    {
        $this->title = $title;
        return $this;
    }
    /**
     * @return string
     */
    public function getDescription()
    {
        return $this->description;
    }
    /**
     * @param string $description
     * @return $this
     */
    public function setDescription($description)
    {
        $this->description = $description;
        return $this;
    }
    /**
     * @return string
     */
    public function getPrice()
    {
        return $this->price;
    }
    /**
     * @param string $price
     * @return $this
     */
    public function setPrice($price)
    {
        $this->price = $price;
        return $this;
    }
    /**
     * @return string
     */
    public function getDifficulty()
    {
        return $this->difficulty;
    }
    /**
     * @param string $difficulty
     * @return $this
     */
    public function setDifficulty($difficulty)
    {
        $this->difficulty = $difficulty;
        return $this;
    }
    /**
     * @return Document[]
     */
    public function getDocuments()
    {
        return $this->documents;
    }
    /**
     * @param Document[] $documents
     * @return $this
     */
    public function setDocuments($documents)
    {
        $this->documents = $documents;
        return $this;
    }
    /**
     * @return Textile
     */
    public function getTextile()
    {
        return $this->textile;
    }
    /**
     * @param Textile $textile
     * @return $this
     */
    public function setTextile($textile)
    {
        $this->textile = $textile;
        return $this;
    }
    /**
     * @return Purpose
     */
    public function getPurpose()
    {
        return $this->purpose;
    }
    /**
     * @param Purpose $purpose
     * @return $this
     */
    public function setPurpose($purpose)
    {
        $this->purpose = $purpose;
        return $this;
    }
    /**
     * @return Gender
     */
    public function getGender()
    {
        return $this->gender;
    }
    /**
     * @param Gender $gender
     * @return $this
     */
    public function setGender($gender)
    {
        $this->gender = $gender;
        return $this;
    }
    /**
     * @return Season
     */
    public function getSeason()
    {
        return $this->season;
    }
    /**
     * @param Season $season
     * @return $this
     */
    public function setSeason($season)
    {
        $this->season = $season;
        return $this;
    }
    /**
     * @return Type
     */
    public function getType()
    {
        return $this->type;
    }
    /**
     * @param Type $type
     * @return $this
     */
    public function setType($type)
    {
        $this->type = $type;
        return $this;
    }
    /**
     * @return Category
     */
    public function getCategory()
    {
        return $this->category;
    }
    /**
     * @param Category $category
     * @return $this
     */
    public function setCategory($category)
    {
        $this->category = $category;
        return $this;
    }
    /**
     * @return Brand
     */
    public function getBrand()
    {
        return $this->brand;
    }
    /**
     * @param Brand $brand
     * @return $this
     */
    public function setBrand($brand)
    {
        $this->brand = $brand;
        return $this;
    }
    /**
     * @return string
     */
    public function isNew()
    {
        return $this->new;
    }
    /**
     * @param string $new
     * @return $this
     */
    public function setNew($new)
    {
        $this->new = $new;
        return $this;
    }
    /**
     * @return string
     */
    public function onSale()
    {
        return $this->sale;
    }
    /**
     * @param string $sale
     * @return $this
     */
    public function setSale($sale)
    {
        $this->sale = $sale;
        return $this;
    }
    /**
     * @return string
     */
    public function isHot()
    {
        return $this->hot;
    }
    /**
     * @param string $hot
     * @return $this
     */
    public function setHot($hot)
    {
        $this->hot = $hot;
        return $this;
    }
    /**
     * @return string
     */
    public function isRecommended()
    {
        return $this->recommended;
    }
    /**
     * @param string $recommended
     * @return $this
     */
    public function setRecommended($recommended)
    {
        $this->recommended = $recommended;
        return $this;
    }
    /**
     * @return string
     */
    public function getLikes()
    {
        return $this->likes;
    }
    /**
     * @param string $likes
     * @return $this
     */
    public function setLikes($likes)
    {
        $this->likes = $likes;
        return $this;
    }
    /**
     * @return boolean
     */
    public function isDeleted()
    {
        return $this->deleted;
    }
    /**
     * @param boolean $deleted
     */
    public function setDeleted($deleted)
    {
        $this->deleted = $deleted;
    }
    /**
     * Normalizes the object into an array of scalars|arrays.
     *
     * It is important to understand that the normalize() call should normalize
     * recursively all child objects of the implementor.
     *
     * @param NormalizerInterface $normalizer The normalizer is given so that you
     *                                        can use it to normalize objects contained within this object.
     * @param string|null $format The format is optionally given to be able to normalize differently
     *                                        based on different output formats.
     * @param array $context Options for normalizing this object
     *
     * @return array
     */
    public function normalize(NormalizerInterface $normalizer, $format = null, array $context = array())
    {
        $result['id']                    = $this->getId();
        $result['title']                 = $this->getTitle();
        $result['description']           = $this->getDescription();
        $result['price']                 = $this->getPrice();
        $result['difficulty']            = $this->getDifficulty();
        $result['documents']             = $normalizer->normalize($this->getDocuments());
        $result['textile']               = $normalizer->normalize($this->getTextile());
        $result['purpose']               = $normalizer->normalize($this->getPurpose());
        $result['gender']                = $normalizer->normalize($this->getGender());
        $result['season']                = $normalizer->normalize($this->getSeason());
        $result['type']                  = $normalizer->normalize($this->getType());
        $result['category']              = $normalizer->normalize($this->getCategory());
        $result['brand']                 = $normalizer->normalize($this->getBrand());
        $result['new']                   = $this->isNew();
        $result['sale']                  = $this->onSale();
        $result['hot']                   = $this->isHot();
        $result['recommended']           = $this->isRecommended();
        $result['likes']                 = $this->getLikes();
        $result['created_at']            = $this->getCreatedAt();
        $result['updated_at']            = $this->getUpdatedAt();
        $result['shoes_models']          = $normalizer->normalize($this->getShoesModels());
        $result['deleted']               = $this->isDeleted();
        $result['class']                 = 'shoes-product';
        return $result;
    }
}

<?php
/**
 * Created by PhpStorm.
 * User: leonid.groshev
 * Date: 21.12.2016
 * Time: 12:31
 */
namespace Atelie\Entity;
use DateTime;
use Doctrine\Common\Collections\ArrayCollection;
use Symfony\Component\Serializer\Normalizer\NormalizableInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
/**
 * Class ShoesModel
 *
 * @package Atelie\Entity
 *
 * @Entity @Table(name="shoes_models")
 * @HasLifecycleCallbacks
 */
class ShoesModel implements NormalizableInterface
{
    /**
     * @var int
     * @Id @Column(type="integer") @GeneratedValue
     */
    protected $id;
    /**
     * @var DateTime
     * @Column(type="datetime")
     */
    protected $created_at;
    /**
     * @var DateTime
     * @Column(type="datetime", nullable = true)
     */
    protected $updated_at;
    /**
     * @var bool
     * @Column(type="boolean", options={"default": false})
     */
    protected $deleted = false;
    /**
     * Relations
     */
    /**
     * @var Document[]|ArrayCollection
     * @ManyToMany(targetEntity="Document")
     */
    protected $documents;
    /**
     * @var ShoesSize
     * @ManyToOne(targetEntity="ShoesSize")
     */
    protected $size;
    /**
     * @var ShoesProduct
     * @ManyToOne(targetEntity="ShoesProduct")
     */
    protected $shoes_product;
    function __construct()
    {
        $this->documents = new ArrayCollection();
    }
    /**
     * @return ShoesProduct
     */
    public function getShoesProduct()
    {
        return $this->shoes_product;
    }
    /**
     * @param ShoesProduct $shoes_product
     * @return $this
     */
    public function setShoesProduct($shoes_product)
    {
        $this->shoes_product = $shoes_product;
        return $this;
    }
    /**
     * @return int
     */
    public function getId()
    {
        return $this->id;
    }
    /**
     * Create and Update time
     * @PrePersist
     * @PreUpdate
     */
    public function updatedTimestamps()
    {
        if ($this->created_at == null) {
            $this->created_at = new DateTime('now');
        }
        else {
            $this->updated_at = new DateTime('now');
        }
    }
    /**
     * @return DateTime
     */
    public function getCreatedAt()
    {
        return $this->created_at;
    }
    /**
     * @return DateTime
     */
    public function getUpdatedAt()
    {
        return $this->updated_at;
    }
    /**
     * @return Document[]
     */
    public function getDocuments()
    {
        return $this->documents;
    }
    /**
     * @param Document[] $documents
     * @return $this
     */
    public function setDocuments($documents)
    {
        $this->documents = $documents;
        return $this;
    }
    /**
     * @return ShoesSize
     */
    public function getShoesSize()
    {
        return $this->size;
    }
    /**
     * @param ShoesSize $size
     * @return $this
     */
    public function setShoesSize($size)
    {
        $this->size = $size;
        return $this;
    }
    /**
     * @return boolean
     */
    public function isDeleted()
    {
        return $this->deleted;
    }
    /**
     * @param boolean $deleted
     */
    public function setDeleted($deleted)
    {
        $this->deleted = $deleted;
    }
    /**
     * Normalizes the object into an array of scalars|arrays.
     *
     * It is important to understand that the normalize() call should normalize
     * recursively all child objects of the implementor.
     *
     * @param NormalizerInterface $normalizer The normalizer is given so that you
     *                                        can use it to normalize objects contained within this object.
     * @param string|null $format The format is optionally given to be able to normalize differently
     *                                        based on different output formats.
     * @param array $context Options for normalizing this object
     *
     * @return array
     */
    public function normalize(NormalizerInterface $normalizer, $format = null, array $context = array())
    {
        $result['id']                    = $this->getId();
        $result['documents']             = $normalizer->normalize($this->getDocuments());
        $result['created_at']            = $this->getCreatedAt();
        $result['updated_at']            = $this->getUpdatedAt();
        $result['size']                  = $normalizer->normalize($this->getShoesSize());
        $result['shoes_product']         = $normalizer->normalize($this->getShoesProduct());
        $result['deleted']               = $this->isDeleted();
        $result['class']                 = 'shoes-product';
        return $result;
    }
}

При использовании связи @OneToMany и вызове метода getShoesModels сервер возвращает ошибку 502.

Если отключить вызов метода getShoesModels - то все работает нормально и возвращает нормальный ответ.

В чем может быть причина?