code: public BuildChangeSet getChangeSet() {
          BuildChangeSet result;
          if (changeSet != null) {
              result = changeSet;
          } else if (changeSets != null && !changeSets.isEmpty()) {
              result = changeSets.get(0);
          } else {
              result = null;
          }
          return result;
      }
docs: Returns the change set of a build if available.
  
  If a build performs several scm checkouts (i.e. pipeline builds), the change set of the first
  checkout is returned. To get the complete list of change sets for all checkouts, use
  {@link #getChangeSets()}
  
  If no checkout is performed, null is returned.
  
  @return The change set of the build.