引数無しコンストラクタをprivateにすると落ちる

> 凄く愚かな事を言ってる気がするけど

play frameworkのモデルは、引数無しコンストラクタをprivateにすると落ちる。

```java:StackTrace
org.hibernate.HibernateException: Javassist Enhancement failed: models.//ClassNameXxx
	at play.db.jpa.GenericModel$JPAQuery.fetch(GenericModel.java:423)
// 省略
	at play.mvc.ActionInvoker.invokeWithContinuation(ActionInvoker.java:557)
	at play.mvc.ActionInvoker.invoke(ActionInvoker.java:508)
	at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:484)
	at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:479)
	at play.mvc.ActionInvoker.invoke(ActionInvoker.java:161)
	... 1 more
Caused by: javax.persistence.PersistenceException: org.hibernate.HibernateException: Javassist Enhancement failed: models.NicoMovie
	at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1389)
	at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1317)
	at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:255)
	at play.db.jpa.GenericModel$JPAQuery.fetch(GenericModel.java:421)
	... 8 more
Caused by: org.hibernate.HibernateException: Javassist Enhancement failed: models.NicoMovie
	at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.getProxy(JavassistLazyInitializer.java:142)
	at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.getProxy(JavassistProxyFactory.java:71)
	at org.hibernate.tuple.entity.AbstractEntityTuplizer.createProxy(AbstractEntityTuplizer.java:631)
	at org.hibernate.persister.entity.AbstractEntityPersister.createProxy(AbstractEntityPersister.java:3737)
	at org.hibernate.event.def.DefaultLoadEventListener.createProxyIfNecessary(DefaultLoadEventListener.java:360)
	at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:281)
	at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:152)
	at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1090)
	at org.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1038)
	at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:630)
	at org.hibernate.type.EntityType.resolve(EntityType.java:438)
	at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:139)
	at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:982)
	at org.hibernate.loader.Loader.doQuery(Loader.java:857)
	at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
	at org.hibernate.loader.Loader.doList(Loader.java:2542)
	at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
	at org.hibernate.loader.Loader.list(Loader.java:2271)
	at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:459)
	at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:365)
	at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
	at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1268)
	at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
	at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:246)
	... 9 more
Caused by: java.lang.InstantiationException: models.NicoMovie_$$_javassist_10
	at java.lang.Class.newInstance0(Class.java:342)
	at java.lang.Class.newInstance(Class.java:310)
	at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.getProxy(JavassistLazyInitializer.java:139)
	... 32 more

```