code: public void setReferences(Map<String, List<UniqueId>> references) {
          if (references != null) {
              this.references = new HashMap<>(references);
          } else {
              this.references = null;
          }
      }
docs: Overrides the references for copies made with this visitor.
  
  @param references a map of reference name to reference pairs, or
  <code>null</code> to use the original proposition's value for this field.