dawn_node: Return undefined for "void" methods instead of null

Bug: dawn:1123
Change-Id: I38a5b160c12485ea23b34a6b3c8cdf44baee2ada
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/75903
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/dawn_node/interop/WebGPU.cpp.tmpl b/src/dawn_node/interop/WebGPU.cpp.tmpl
index d55dd3f..f70df8e 100644
--- a/src/dawn_node/interop/WebGPU.cpp.tmpl
+++ b/src/dawn_node/interop/WebGPU.cpp.tmpl
@@ -206,7 +206,7 @@
 {{-      if not (IsUndefinedType $o.Type) }}auto result = {{end -}}
           impl->{{$o.Name}}(info.Env(){{range $i, $_ := $o.Parameters}}, std::get<{{$i}}>(args){{end}});
           {{/* indent */ -}}
-{{-      if   IsUndefinedType $o.Type}}return info.Env().Null();
+{{-      if   IsUndefinedType $o.Type}}return info.Env().Undefined();
 {{-      else                        }}return ToJS(info.Env(), result);
 {{-      end                         }}
         }