Issue 28027. Move Null to the bottom in the Analyzer.

pkg/analyzer/lib/src/summary/link.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 229 matching lines @@
       return result;
     }
     // TODO(paulberry): implement other cases.
     throw new UnimplementedError('${element.runtimeType}');
   }
   // TODO(paulberry): implement other cases.
   throw new UnimplementedError('${type.runtimeType}');
 }
 
 DartType _dynamicIfNull(DartType type) {
-  if (type == null || type.isBottom || type.isVoid) {
+  if (type == null || type.isBottom || type.isDartCoreNull || type.isVoid) {
     return DynamicTypeImpl.instance;
   }
   return type;
 }
 
 /**
  * Create an [UnlinkedParam] representing the given [parameter], which should be
  * a parameter of a synthetic function type (e.g. one produced during type
  * inference as a result of computing the least upper bound of two function
  * types).
@@ skipping 1738 matching lines @@
           break;
         case UnlinkedExprOperation.concatenate:
           stack.length -= _getNextInt();
           stack.add(typeProvider.stringType);
           break;
         case UnlinkedExprOperation.makeSymbol:
           strPtr++;
           stack.add(typeProvider.symbolType);
           break;
         case UnlinkedExprOperation.pushNull:
-          stack.add(BottomTypeImpl.instance);
+          stack.add(typeProvider.nullType);
           break;
         case UnlinkedExprOperation.pushReference:
           _doPushReference();
           break;
         case UnlinkedExprOperation.extractProperty:
           _doExtractProperty();
           break;
         case UnlinkedExprOperation.invokeConstructor:
           _doInvokeConstructor();
           break;
@@ skipping 2929 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementMixin get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }