ReferenceError on undefined returns

[kiranshila]

Many of the Espruino commands that are side-effecting return undefined. I believe in CLJS this should return nil. However, in the Esprit REPL, it throws a reference error.

cljs.user=> js/undefined
ReferenceError: "0" is not defined
 at line 13 col 7
throw e__6755__auto__;
      ^
in function called from line 14 col 5
}})()
   ^
at line 1 col 89
...tus:"success",value:eval(d)}}catch(f){var a=f;return{status:...

[kiranshila]

This is the same problem as #3 but is the case for js/undefined in general, not just write calls.