protected final String getDefaultScheme() {
        String defaultScheme = this.properties.getDefaultScheme();
        if (defaultScheme == null) {
            return null;
        }

        return defaultScheme.contains(":") ? defaultScheme : defaultScheme + ":///";
    }
Gets the default scheme that should be used for a client channel's target if no address is specified for a
client's channel properties.

@return The default scheme defined in {@link GrpcChannelsProperties}.
grpc-client-spring-boot-starter/src/main/java/net/devh/boot/grpc/client/channelfactory/AbstractChannelFactory.java