code: public <T> String resolveApitraryEntityId(T entity) {
  		if (entity == null) {
  			throw new ApitraryOrmIdDefinitionsException("Apitrary entity has not to be null.");
  		}
  		List<java.lang.reflect.Field> fields = ClassUtil.getAnnotatedFields(entity.getClass(), Id.class);
  		if (fields.isEmpty()) {
  			throw new ApitraryOrmIdDefinitionsException("Apitrary entity must own an annotated ID field.");
  		}
  		if (fields.size() > 1) {
  			throw new ApitraryOrmIdDefinitionsException("Apitrary entity can not have more than one ID field.");
  		}
  
  		java.lang.reflect.Field field = fields.get(0);
  		String id = ClassUtil.getValueOf(field, entity, entity.getClass(), String.class);
  		if (id == null || id.isEmpty()) {
  			throw new ApitraryOrmIdException("Entity lacks ID and is probably not persisted.");
  		}
  		return id;
  	}
docs: <p>
  resolveApitraryEntityId.
  </p>
  
  @param entity
  a T object.
  @param <T>
  a T object.
  @return a {@link java.lang.String} object.