Fix missing cases of empty_string canonicalization

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 07b967f2b8cf3bf37e093d1e3724b142d50663ad..1188bda43a976bb4f9b75ddba8fdeb0d96d8b8ff 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -6723,11 +6723,15 @@ MaybeLocal<String> v8::String::NewExternalTwoByte(
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
   ENTER_V8_NO_SCRIPT_NO_EXCEPTION(i_isolate);
   LOG_API(i_isolate, String, NewExternalTwoByte);
-  i::Handle<i::String> string = i_isolate->factory()
-                                    ->NewExternalStringFromTwoByte(resource)
-                                    .ToHandleChecked();
-  i_isolate->heap()->RegisterExternalString(*string);
-  return Utils::ToLocal(string);
+  if (resource->length() > 0) {
+    i::Handle<i::String> string = i_isolate->factory()
+                                      ->NewExternalStringFromTwoByte(resource)
+                                      .ToHandleChecked();
+    i_isolate->heap()->RegisterExternalString(*string);
+    return Utils::ToLocal(string);
+  } else {
+    return Utils::ToLocal(i_isolate->factory()->empty_string());
+  }
 }
 
 
@@ -6747,11 +6751,15 @@ MaybeLocal<String> v8::String::NewExternalOneByte(
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
   ENTER_V8_NO_SCRIPT_NO_EXCEPTION(i_isolate);
   LOG_API(i_isolate, String, NewExternalOneByte);
-  i::Handle<i::String> string = i_isolate->factory()
-                                    ->NewExternalStringFromOneByte(resource)
-                                    .ToHandleChecked();
-  i_isolate->heap()->RegisterExternalString(*string);
-  return Utils::ToLocal(string);
+  if (resource->length() > 0) {
+    i::Handle<i::String> string = i_isolate->factory()
+                                      ->NewExternalStringFromOneByte(resource)
+                                      .ToHandleChecked();
+    i_isolate->heap()->RegisterExternalString(*string);
+    return Utils::ToLocal(string);
+  } else {
+    return Utils::ToLocal(i_isolate->factory()->empty_string());
+  }
 }