address review comments

Author: eklavya

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -920,7 +920,8 @@ object desugar {
     assert(arity <= Definitions.MaxTupleArity)
     def tupleTypeRef = defn.TupleType(arity)
     if (arity == 1) ts.head
-    else if (arity == 0) unitLiteral
+    else if (arity == 0)
+      if (ctx.mode is Mode.Type) TypeTree(defn.UnitType) else unitLiteral
     else if (ctx.mode is Mode.Type) AppliedTypeTree(ref(tupleTypeRef), ts)
     else Apply(ref(tupleTypeRef.classSymbol.companionModule.termRef), ts)
   }