private void encodeLearners(final PBLogEntry.Builder builder, final List<PeerId> learners) {
        final int size = learners.size();
        for (int i = 0; i < size; i++) {
            builder.addLearners(ZeroByteStringHelper.wrap(AsciiStringUtil.unsafeEncode(learners.get(i).toString())));
        }
    }
V2 log entry encoder based on protobuf, see src/main/resources/log.proto

@author boyan(boyan@antfin.com)
jraft-core/src/main/java/com/alipay/sofa/jraft/entity/codec/v2/V2Encoder.java