gjs tries to free NULL error returned from C function

System information

What is your operating system and version? macOS 10.15.6

What is your version of GJS? 1.64.4 (homebrew package)

Bug information

Steps to reproduce

I've written a library which includes the following function:

/**
 * htsp_message_to_error:
 * @msg: (transfer none):
 * Returns: (transfer full) (nullable):
 *
 * Makes a GError from a message with an error field. Returns NULL if the
 * message doesn't have an error field.
 */
GError *htsp_message_to_error(const GstStructure *msg);

Current behaviour

What happened that made it evident there was a problem?

When I called the above function from gjs I saw a warning on the console that it had tried to call g_error_free() on a NULL pointer, and worked out that the problem call was in gjs, not my code. Sorry, I didn't keep an exact log of the warning, but it was definitely about g_error_free and NULL. I got a backtrace by using G_MESSAGES_DEBUG=all, but it's a bit limited. If you need something more detailed I can try rebuilding gjs with debugging symbols on Linux and using the spidermonkey debugger.

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libglib-2.0.0.dylib           	0x0000000102534d2e g_logv + 1070
1   libglib-2.0.0.dylib           	0x00000001025348e2 g_log + 130
2   libgjs.0.dylib                	0x000000010217ae0a gjs_g_arg_release_internal(JSContext*, GITransfer, _GIBaseInfoStub*, GITypeTag, _GIArgument*) + 186
3   libgjs.0.dylib                	0x000000010217ad3d gjs_g_argument_release(JSContext*, GITransfer, _GIBaseInfoStub*, _GIArgument*) + 77
4   libgjs.0.dylib                	0x00000001021a3728 gjs_invoke_c_function(JSContext*, Function*, JS::Handle<JSObject*>, JS::HandleValueArray const&, mozilla::Maybe<JS::MutableHandle<JS::Value> >, _GIArgument*) + 8088
5   libgjs.0.dylib                	0x00000001021a520d function_call(JSContext*, unsigned int, JS::Value*) + 765
6   libmozjs-68.dylib             	0x00000001028b6781 js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct) + 2161