public void setNegotiationType(final NegotiationType negotiationType) {
        this.negotiationType = negotiationType;
    }
Sets the negotiation type to use on the connection. Either of {@link NegotiationType#TLS TLS} (recommended),
{@link NegotiationType#PLAINTEXT_UPGRADE PLAINTEXT_UPGRADE} or {@link NegotiationType#PLAINTEXT PLAINTEXT}.
Defaults to TLS.

@param negotiationType The negotiation type to use or null to use the fallback.
grpc-client-spring-boot-starter/src/main/java/net/devh/boot/grpc/client/config/GrpcChannelProperties.java