code: protected void processRemainingReferences(APMSpanBuilder builder, Reference primaryRef) {
          // Check if other references
          for (Reference ref : builder.references) {
              if (primaryRef == ref) {
                  continue;
              }
              // Setup correlation ids for other references
              if (ref.getReferredTo() instanceof APMSpan) {
                  APMSpan referenced = (APMSpan) ref.getReferredTo();
  
                  String nodeId = referenced.getNodePath();
                  getNodeBuilder().addCorrelationId(new CorrelationIdentifier(Scope.CausedBy, nodeId));
  
              } else if (ref.getReferredTo() instanceof APMSpanBuilder
                      && ((APMSpanBuilder) ref.getReferredTo()).state().containsKey(Constants.HAWKULAR_APM_ID)) {
                  getNodeBuilder().addCorrelationId(new CorrelationIdentifier(Scope.Interaction,
                          ((APMSpanBuilder) ref.getReferredTo()).state().get(Constants.HAWKULAR_APM_ID).toString()));
              }
          }
      }
docs: This method processes the remaining references by creating appropriate correlation ids
  against the current node.
  
  @param builder    The span builder
  @param primaryRef The primary reference, if null if one was not found