Always store the type of a conditional expression on the node.

testcases/input/null_aware.dart

Index: testcases/input/null_aware.dart
diff --git a/testcases/input/null_aware.dart b/testcases/input/null_aware.dart
new file mode 100644
index 0000000000000000000000000000000000000000..bb1e3e0dd01346ec57ca7d3925e602b852ed08ac
--- /dev/null
+++ b/testcases/input/null_aware.dart
@@ -0,0 +1,20 @@
+// 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.
+class Foo {
+  int field;
+  static int staticField;
+}
+
+main() {
+  Foo foo = new Foo();
+  foo?.field = 5;
+  Foo?.staticField = 5;
+  foo.field ??= 5;
+  Foo.staticField ??= 5;
+  foo?.field ??= 5;
+  Foo?.staticField ??= 5;
+
+  int intValue = foo.field ?? 6;
+  num numValue = foo.field ?? 4.5;
+}