key    string
	}{
		{[]interface{}{"a"}, "a"},
		{[]interface{}{1, 2, 3}, "1_2_3"},
		{[]interface{}{1, nil, 3}, "1_nil_3"},
		{[]interface{}{[]interface{}{1, 2, 3}}, "[1 2 3]"},
		{[]interface{}{[]interface{}{"1", "2", "3"}}, "[1 2 3]"},
		{[]interface{}{[]interface{}{"1", nil, "3"}}, "[1 <nil> 3]"},
	}
	for _, c := range cases {
		if key := ToStringKey(c.values...); key != c.key {