public Collection<RoundChange> createRoundChangeCertificate() {
      if (roundChangeReady()) {
        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/ibft/src/main/java/org/hyperledger/besu/consensus/ibft/statemachine/RoundChangeManager.java