REPL crash when toString returns null

[bishabosha]

Compiler version

3.2.2

Minimized code

scala> class Foo { override def toString = null }
// defined class Foo
                                                                                                                 
scala> new Foo()

Output (click arrow to expand)

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.length()" because "str" is null
	at dotty.tools.repl.Rendering.truncate(Rendering.scala:92)
	at dotty.tools.repl.Rendering.classLoader$$anonfun$1(Rendering.scala:79)
	at dotty.tools.repl.Rendering.classLoader$$anonfun$adapted$1(Rendering.scala:85)
	at dotty.tools.repl.Rendering.replStringOf(Rendering.scala:102)
	at dotty.tools.repl.Rendering.$anonfun$5(Rendering.scala:115)
	at scala.Option.map(Option.scala:242)
	at dotty.tools.repl.Rendering.valueOf(Rendering.scala:115)
	at dotty.tools.repl.Rendering.renderVal(Rendering.scala:157)
	at dotty.tools.repl.ReplDriver.$anonfun$7(ReplDriver.scala:365)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.repl.ReplDriver.extractAndFormatMembers$1(ReplDriver.scala:371)
	at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:403)
	at scala.Option.map(Option.scala:242)
	at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:409)
	at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:307)
	at scala.util.Either.fold(Either.scala:189)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:323)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:248)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:168)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:171)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:191)
	at dotty.tools.repl.ReplDriver.runBody$$anonfun$1(ReplDriver.scala:179)
	at dotty.tools.runner.ScalaClassLoader$.asContext(ScalaClassLoader.scala:80)
	at dotty.tools.repl.ReplDriver.runBody(ReplDriver.scala:179)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:171)
	at dotty.tools.repl.ReplDriver.tryRunning(ReplDriver.scala:133)
	at dotty.tools.repl.Main$.main(Main.scala:7)
	at dotty.tools.repl.Main.main(Main.scala)

Expectation

Scala 2.13 prints the following:

scala> class Foo { override def toString = null }
class Foo

scala> new Foo()
val res0: Foo = null toString

[som-snytt]

Handled correctly in 3.2.1, but not by truncation check.

[som-snytt]

I submitted a quick PR as a refresher in using Scala 3 syntax to write Scala 3 tests.