example1.epp

<% |
  Optional[String] $es_protocol      = undef,
  Integer          $es_major_version = 0
| -%>
 

<% if $es_protocol {
    $_es_protocol = $es_protocol
  }
  else {
    $_es_protocol = $es_major_version ? {
      5       => 'https',
      default => 'http'
    }
  }
%>

example2.epp

<% |
  Integer          $es_major_version = 0,
  Optional[String] $es_protocol      = $es_major_version ? { 5 => 'https', default => 'http' },
| -%>