code: public void complete() {
          long seqNo = this.operation.getSequenceNumber();
          Preconditions.checkState(seqNo >= 0, "About to complete a CompletableOperation that has no sequence number.");
  
          this.done = true;
          if (this.successHandler != null) {
              Callbacks.invokeSafely(this.successHandler, null, cex -> log.error("Success Callback invocation failure.", cex));
          }
      }
docs: Completes the operation (no exception).