public Set<PeerId> listLearners() {
        final Set<PeerId> ret = new HashSet<>(this.conf.getLearners());
        ret.addAll(this.oldConf.getLearners());
        return ret;
    }
Returns true when the conf entry is valid.

@return if the the entry is valid
jraft-core/src/main/java/com/alipay/sofa/jraft/conf/ConfigurationEntry.java