Open up the REPL type Set(), and press tab gives the following error.

Welcome to Scala version 2.10.0-M3 (OpenJDK 64-Bit Server VM, Java 1.7.0-u4-b228).
Type in expressions to have them evaluated.
Type :help for more information.

scala> Set()exception when typing $line2.$read.$iw.$iw.$intp()
exception when typing scala.runtime.ScalaRunTime.replStringOf($line2.$read.$iw.$iw.$intp(), 1000)
exception when typing "$intp: scala.tools.nsc.interpreter.IMain = ".+(scala.runtime.ScalaRunTime.replStringOf($line2.$read.$iw.$iw.$intp(), 1000))
exception when typing {
$read.$iw.$iw;
"$intp: scala.tools.nsc.interpreter.IMain = ".+(scala.runtime.ScalaRunTime.replStringOf($line2.$read.$iw.$iw.$intp(), 1000))
}
exception when typing private[this] val $print: String = {
$read.$iw.$iw;
"$intp: scala.tools.nsc.interpreter.IMain = ".+(scala.runtime.ScalaRunTime.replStringOf($line2.$read.$iw.$iw.$intp(), 1000))
}
exception when typing object $eval extends Object {
def (): $line2.$eval.type = {
$eval.super.();
()
};
lazy private[this] var $result: scala.tools.nsc.interpreter.IMain = _;
lazy def $result(): scala.tools.nsc.interpreter.IMain = {
$eval.this.$result = $line2.$read.$iw.$iw.$intp();
$eval.this.$result
};
private[this] val $print: String = {
$read.$iw.$iw;
"$intp: scala.tools.nsc.interpreter.IMain = ".+(scala.runtime.ScalaRunTime.replStringOf($line2.$read.$iw.$iw.$intp(), 1000))
};
def $print(): String = $eval.this.$print
}
exception when typing package $line2 {
object $eval extends Object {
def (): $line2.$eval.type = {
$eval.super.();
()
};
lazy private[this] var $result: scala.tools.nsc.interpreter.IMain = _;
lazy def $result(): scala.tools.nsc.interpreter.IMain = {
$eval.this.$result = $line2.$read.$iw.$iw.$intp();
$eval.this.$result
};
private[this] val $print: String = {
$read.$iw.$iw;
"$intp: scala.tools.nsc.interpreter.IMain = ".+(scala.runtime.ScalaRunTime.replStringOf($line2.$read.$iw.$iw.$intp(), 1000))
};
def $print(): String = $eval.this.$print
}
}

 while compiling:  <console>
   current phase:  erasure
 library version:  version 2.10.0-M3
compiler version:  version 2.10.0-M3

reconstructed args:

unhandled exception while transforming
error:
while compiling:
current phase: erasure
library version: version 2.10.0-M3
compiler version: version 2.10.0-M3
reconstructed args:

uncaught exception during compilation: java.lang.NullPointerException