Throwable constructor parameter message should be nullable string

Cherry-picked from:
https://github.com/develar/kotlin/commit/7604aa2a0f21a3fa78d94bbabc0f8a6c140c14e4
https://github.com/develar/kotlin/commit/578d51f783bce7da71f08e21706517416ed9f7a6

js/js.libraries/src/core/javalang.kt

@@ -4,25 +4,25 @@ import java.io.IOException
 import js.library
 
 library
-open public class Exception() : Throwable() {}
+open public class Exception(message: String? = null) : Throwable() {}
 
 library("splitString")
 public fun String.split(regex : String) : Array<String> = js.noImpl
 
 library
-public class IllegalArgumentException(message: String = "") : Exception() {}
+public class IllegalArgumentException(message: String? = null) : Exception() {}
 
 library
-public class IllegalStateException(message: String = "") : Exception() {}
+public class IllegalStateException(message: String? = null) : Exception() {}
 
 library
-public class IndexOutOfBoundsException(message: String = "") : Exception() {}
+public class IndexOutOfBoundsException(message: String? = null) : Exception() {}
 
 library
-public class UnsupportedOperationException(message: String = "") : Exception() {}
+public class UnsupportedOperationException(message: String? = null) : Exception() {}
 
 library
-public class NumberFormatException(message: String = "") : Exception() {}
+public class NumberFormatException(message: String? = null) : Exception() {}
 
 library
 public trait Runnable {