code: @Override
      public T findOne(EntityFilter<T> filter) {
          for (T object : findAll()) {
              if (filter.accept(object)) {
                  return object;
              }
          }
          return null;
      }
docs: Retrieves the entity matching the given filter. If several entities matches, the first is returned.
  
  @param filter the filter
  @return the first matching instance, {@literal null} if none