public Collection<RoundChange> createRoundChangeCertificate() {
      if (roundChangeQuorumReceived()) {
        actioned = true;
        return receivedMessages.values();
      } else {
        throw new IllegalStateException("Unable to create RoundChangeCertificate at this time.");
      }
    }
Create round change certificate collection.

@return the collection
consensus/qbft-core/src/main/java/org/hyperledger/besu/consensus/qbft/core/statemachine/RoundChangeManager.java