private void checkPeers(final Collection<PeerId> peers) {
        for (final PeerId peer : peers) {
            Requires.requireNonNull(peer, "Null peer in collection");
        }
    }
Cli service implementation.

@author boyan (boyan@alibaba-inc.com)
@author jiachun.fjc
jraft-core/src/main/java/com/alipay/sofa/jraft/core/CliServiceImpl.java