enum list - doesn't handle an empty list

This uses `string:split/3` - but what if it is a list of 0 or more atoms, not 1 or more:

```erlang
1> string:split("a,b,c",",",all).
["a","b","c"]
2> string:split("a",",",all).
["a"]
3> string:split("",",",all).
[[]]
```

If it uses `string:lexemes/2` ...

```erlang
5> string:lexemes("a,b,c",",").
["a","b","c"]
6> string:lexemes("a",",").
["a"]
7> string:lexemes("",",").
[]
```