code: protected <E extends Identifiable> E findEntity(EntityManager em, BigInteger id, Class<E> type) {
  		requireArgument(em != null, "The entity manager cannot be null.");
  		requireArgument(id != null && id.compareTo(ZERO) > 0, "ID must be positive and non-zero");
  		requireArgument(type != null, "The entity cannot be null.");
  		em.getEntityManagerFactory().getCache().evictAll();
  		return em.find(type, id);
  	}
docs: Locates an entity based on it's primary key value.
  
  @param   <E>   The type of the entity.
  @param   em    The entity manager to use. Cannot be null.
  @param   id    The primary key of the entity. Cannot be null and must be a positive non-zero number.
  @param   type  The runtime type of the entity. Cannot be null.
  
  @return  The entity or null if no entity exists for the primary key.