When net.ssl.allowConnectionsWithoutCertificates: true every client connection using no SSL certificate produces a warning message in the log:

2016-XX-XXTXX:XX:XX.XXX+0000 W NETWORK [connXXXX] no SSL certificate provided by peer

It would be nice if it is possible to suppress those warnings, as SSL connections with no client certificates are enabled explicitly by setting net.ssl.allowConnectionsWithoutCertificates: true.