How can I get values from listOf param in kotlin DSL?

Question

I have a BuildType with this param:

select(
                name = "services_to_deploy",
                value = "",
                label = "Services to deploy",
                display = ParameterDisplay.PROMPT,
                allowMultiple = true,
                options = listOf(
                    "Service1" to """front""",
                    "Service2" to """back""",
                    "Service3" to """other"""
            )

I can get list of services_to_deploy, If a do echo %services_to_deploy% And it would be "front,back,other"

And how can I get list where would be "Service1,Service2,Service3"?