private void unlockId() {
        if (this.id == null) {
            return;
        }
        this.id.unlock();
    }
Send log entries to follower, returns true when success, otherwise false and unlock the id.

@param nextSendingIndex next sending index
@return send result.
jraft-core/src/main/java/com/alipay/sofa/jraft/core/Replicator.java