Refactor conditions

We special completion on qualifiers of type Nothing to not return the method on Any.
Also special case completion on qualifiers of type Null to not return completion that involves implicit conversions.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -210,13 +210,9 @@ object Completion {
      * considered.
      */
     def addMemberCompletions(qual: Tree)(implicit ctx: Context): Unit = {
-      if (qual.tpe =:= defn.NothingType)
-        ()
-      else if (qual.tpe.isRef(defn.NullClass))
-        addAccessibleMembers(defn.AnyRefType)
-      else {
+      if (!qual.tpe.widenDealias.isBottomType) {
         addAccessibleMembers(qual.tpe)
-        if (!mode.is(Mode.Import)) {
+        if (!mode.is(Mode.Import) && !qual.tpe.isRef(defn.NullClass)) {
           // Implicit conversions do not kick in when importing
           implicitConversionTargets(qual)(ctx.fresh.setExploreTyperState())
             .foreach(addAccessibleMembers)