presto-resource-group-managers/src/main/java/io/prestosql/plugin/resourcegroups/ResourceGroupNameTemplate.java/NameFragment/NameFragment
class NameFragment:        private NameFragment(String variable, String literal)
        {
            checkArgument((variable == null) ^ (literal == null), "only one of variable or literal can be defined");
            this.variable = variable;
            this.literal = literal;
        }