revert change to sourcePos

Author: noti0na1

compiler/src/dotty/tools/dotc/util/SourcePosition.scala

@@ -2,8 +2,6 @@ package dotty.tools
 package dotc
 package util
 
-import scala.language.{unsafeNulls => _}
-
 import printing.{Showable, Printer}
 import printing.Texts._
 import core.Contexts.Context
@@ -67,7 +65,7 @@ extends SrcPos, interfaces.SourcePosition, Showable {
   def toSynthetic: SourcePosition = withSpan(span.toSynthetic)
 
   def outermost: SourcePosition =
-    if outer == NoSourcePosition then this else outer.outermost
+    if outer == null || outer == NoSourcePosition then this else outer.outermost
 
   /** Inner most position that is contained within the `outermost` position.
    *  Most precise position that comes from the call site.
@@ -87,7 +85,7 @@ extends SrcPos, interfaces.SourcePosition, Showable {
 }
 
 /** A sentinel for a non-existing source position */
-@sharable object NoSourcePosition extends SourcePosition(NoSource, NoSpan) {
+@sharable object NoSourcePosition extends SourcePosition(NoSource, NoSpan, null) {
   override def line: Int = -1
   override def column: Int = -1
   override def toString: String = "?"