Use Object::null_object() instead of Object::ZoneHandle() when a null object

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
===================================================================
--- runtime/vm/intermediate_language_x64.cc	(revision 37955)
+++ runtime/vm/intermediate_language_x64.cc	(working copy)
@@ -729,7 +729,7 @@
     (argc_tag & NativeArguments::AutoSetupScopeMask()) == 0;
 
   // Push the result place holder initialized to NULL.
-  __ PushObject(Object::ZoneHandle(), PP);
+  __ PushObject(Object::null_object(), PP);
   // Pass a pointer to the first argument in RAX.
   if (!function().HasOptionalParameters()) {
     __ leaq(RAX, Address(RBP, (kParamEndSlotFromFp +
@@ -2001,7 +2001,7 @@
       Label slow_path, done;
       InlineArrayAllocation(compiler, length, &slow_path, &done);
       __ Bind(&slow_path);
-      __ PushObject(Object::ZoneHandle(), PP);  // Make room for the result.
+      __ PushObject(Object::null_object(), PP);  // Make room for the result.
       __ pushq(kLengthReg);
       __ pushq(kElemTypeReg);
       compiler->GenerateRuntimeCall(token_pos(),
@@ -2286,7 +2286,7 @@
 
   // 'instantiator_reg' is the instantiator TypeArguments object (or null).
   // A runtime call to instantiate the type is required.
-  __ PushObject(Object::ZoneHandle(), PP);  // Make room for the result.
+  __ PushObject(Object::null_object(), PP);  // Make room for the result.
   __ PushObject(type(), PP);
   __ pushq(instantiator_reg);  // Push instantiator type arguments.
   compiler->GenerateRuntimeCall(token_pos(),
@@ -2357,7 +2357,7 @@
   __ Bind(&slow_case);
   // Instantiate non-null type arguments.
   // A runtime call to instantiate the type arguments is required.
-  __ PushObject(Object::ZoneHandle(), PP);  // Make room for the result.
+  __ PushObject(Object::null_object(), PP);  // Make room for the result.
   __ PushObject(type_arguments(), PP);
   __ pushq(instantiator_reg);  // Push instantiator type arguments.
   compiler->GenerateRuntimeCall(token_pos(),
@@ -2413,7 +2413,7 @@
   Register context_value = locs()->in(0).reg();
   Register result = locs()->out(0).reg();
 
-  __ PushObject(Object::ZoneHandle(), PP);  // Make room for the result.
+  __ PushObject(Object::null_object(), PP);  // Make room for the result.
   __ pushq(context_value);
   compiler->GenerateRuntimeCall(token_pos(),
                                 deopt_id(),