code: public List<IProcessableOption> getMarkedForProcessing(final String processingKey) {
          List<IProcessableOption> result = this.processingRegistry.get(processingKey);
          if (result == null) {
              return new ArrayList<IProcessableOption>();
          } else {
              return result;
          }
      }
docs: Returns the {@link IProcessableOption}s that were marked by calling
  {@link #markForProcessing(IProcessableOption)} with the given key.
  
  @param processingKey the key with which the options in questions were marked.
  @return list of marked {@link IProcessableOption}s, or an empty list, if
  none were marked