code: public List<BuildChangeSet> getChangeSets() {
          List<BuildChangeSet> result;
          if (changeSets != null) {
              result = changeSets;
          } else if (changeSet != null) {
              result = Collections.singletonList(changeSet);
          } else {
              result = null;
  	}
          return result;
      }
docs: Returns the complete list of change sets for all checkout the build has performed. If no
  checkouts have been performed, returns null.
  
  @return The complete list of change sets of the build.