code: Timer complete() {
          Preconditions.checkState(this.entryId.get() >= 0, "entryId not set; cannot complete Write.");
          this.failureCause.set(null);
          this.result.complete(new LedgerAddress(this.writeLedger.get().metadata, this.entryId.get()));
          return endAttempt();
      }
docs: Indicates that this write completed successfully. This will set the final result on the externalCompletion future.