it fails if passing an empty parameter to a script

[dportabella]

Test.sc:

@main
def main(name: String) { ??? }

$ amm Test.sc john
# ok, as expected

$ amm Test.sc ""
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0
	at java.lang.String.charAt(String.java:658)
	at scala.collection.immutable.StringOps$.apply$extension(StringOps.scala:37)
	at ammonite.main.Router$EntryPoint$$anonfun$invoke$2.apply(Router.scala:79)
	at ammonite.main.Router$EntryPoint$$anonfun$invoke$2.apply(Router.scala:75)
	at scala.collection.Iterator$class.foreach(Iterator.scala:891)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1334)
	at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
	at ammonite.main.Router$EntryPoint.invoke(Router.scala:75)
	at ammonite.main.Scripts$.runMainMethod(Scripts.scala:182)
	at ammonite.main.Scripts$$anonfun$runScript$1$$anonfun$apply$1$$anonfun$apply$3$$anonfun$apply$4.apply(Scripts.scala:96)
	at ammonite.main.Scripts$$anonfun$runScript$1$$anonfun$apply$1$$anonfun$apply$3$$anonfun$apply$4.apply(Scripts.scala:83)
	at ammonite.util.Util$.withContextClassloader(Util.scala:16)
	at ammonite.main.Scripts$$anonfun$runScript$1$$anonfun$apply$1$$anonfun$apply$3.apply(Scripts.scala:82)
	at ammonite.main.Scripts$$anonfun$runScript$1$$anonfun$apply$1$$anonfun$apply$3.apply(Scripts.scala:65)
	at ammonite.util.Res$Success.flatMap(Res.scala:56)
	at ammonite.main.Scripts$$anonfun$runScript$1$$anonfun$apply$1.apply(Scripts.scala:65)
	at ammonite.main.Scripts$$anonfun$runScript$1$$anonfun$apply$1.apply(Scripts.scala:45)
	at ammonite.util.Res$Success.flatMap(Res.scala:56)
	at ammonite.main.Scripts$$anonfun$runScript$1.apply(Scripts.scala:45)
	at ammonite.main.Scripts$$anonfun$runScript$1.apply(Scripts.scala:42)
	at ammonite.util.Res$Success.flatMap(Res.scala:56)
	at ammonite.main.Scripts$.runScript(Scripts.scala:42)
	at ammonite.Main.runScript(Main.scala:210)
	at ammonite.MainRunner$$anonfun$runScript$1.apply(Main.scala:350)
	at ammonite.MainRunner$$anonfun$runScript$1.apply(Main.scala:350)
	at ammonite.MainRunner.watchLoop(Main.scala:336)
	at ammonite.MainRunner.runScript(Main.scala:347)
	at ammonite.Main$.main0(Main.scala:290)
	at ammonite.Main$.main(Main.scala:241)
	at ammonite.Main.main(Main.scala)