typed.go
func (t Typed) StringMust(key string) string {
	s, exists := t.StringIf(key)
	if exists == false {
		panic("expected string value for " + key)
	}
	return s
}
func (t Typed) StringMust(key string) string {
	s, exists := t.StringIf(key)
	if exists == false {
		panic("expected string value for " + key)
	}
	return s
}
// Returns an string or panics