public Nullability(SessionImplementor session) 
{
		this.session = session;
}

 public  void checkNullability(Object[] values,
    EntityPersister persister,
    boolean isUpdate) throws HibernateException, PropertyValueException 
{
		/*
		  * Algorithm
		  * Check for any level one nullability breaks
		  * Look at non null components to
		  *   recursively check next level of nullability breaks
		  * Look at Collections contraining component to
		  *   recursively check next level of nullability breaks
		  *
		  *
		  * In the previous implementation, not-null stuffs where checked
		  * filtering by level one only updateable
		  * or insertable columns. So setting a sub component as update="false"
		  * has no effect on not-null check if the main component had good checkeability
		  * In this implementation, we keep this feature.
		  * However, I never see any documentation mentioning that, but it's for
		  * sure a limitation.
		  */
		final boolean[] nullability = persister.getPropertyNullability();
		final boolean[] checkability = isUpdate ?
			persister.getPropertyUpdateability() :
			persister.getPropertyInsertability();
		final Type[] propertyTypes = persister.getPropertyTypes();
		for ( int i = 0; i <  values.length; i++ ) {
			if ( checkability[i] && values[i]!=LazyPropertyInitializer.UNFETCHED_PROPERTY ) {
				final Object value = values[i];
				if ( !nullability[i] && value == null ) {
					//check basic level one nullablilty
					throw new PropertyValueException(
							"not-null property references a null or transient value",
							persister.getEntityName(),
							persister.getPropertyNames()[i]
						);
				}
				else if ( value != null ) {
					//values is not null and is checkable, we'll look deeper
					String breakProperties = checkSubElementsNullability( propertyTypes[i], value );
					if ( breakProperties != null ) {
						throw new PropertyValueException(
							"not-null property references a null or transient value",
							persister.getEntityName(),
							buildPropertyPath( persister.getPropertyNames()[i], breakProperties )
						);
					}
				}
			}
		}
}

Check nullability of the class persister properties