code: public Object find(Class clazz, Object identifier) {
          EntityManager entityManager = null;
          try {
              entityManager = entityManagers.poll();
              //noinspection unchecked
              return entityManager.find(clazz, identifier);
          } catch (Exception e) {
              e.printStackTrace();
          }
          finally {
              if(entityManager != null)
                  entityManagers.add(entityManager);
          }
  
          return null;
      }
docs: Find an entity with a given type and primary key
  
  @param clazz Entity type
  @param identifier Entity's primary key
  @return Object within database if found