Make FieldType::None() non-nullptr value to avoid undefined behaviour

src/field-type.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/field-type.h"
 
 #include "src/handles-inl.h"
 #include "src/ostreams.h"
 #include "src/types.h"
 
 namespace v8 {
 namespace internal {
 
 // static
 FieldType* FieldType::None() {
-  return reinterpret_cast<FieldType*>(Smi::FromInt(0));
+  // Do not Smi::FromInt(0) here or for Any(), as that may translate
+  // as `nullptr` which is not a valid value for `this`.
+  return reinterpret_cast<FieldType*>(Smi::FromInt(2));
 }
 
 // static
 FieldType* FieldType::Any() {
   return reinterpret_cast<FieldType*>(Smi::FromInt(1));
 }
 
 // static
 Handle<FieldType> FieldType::None(Isolate* isolate) {
   return handle(None(), isolate);
@@ skipping 55 matching lines @@
   } else if (IsNone()) {
     os << "None";
   } else {
     DCHECK(IsClass());
     os << "Class(" << static_cast<void*>(*AsClass()) << ")";
   }
 }
 
 }  // namespace internal
 }  // namespace v8