WebKit2.JavascriptResult.get_value() throws exception "TypeError: Couldn't find foreign struct converter for 'JavaScriptCore.Value'".

I am writing a python3 + webkit2 + gtk3 based GUI. Everything works fine, but when I tried to use WebKit2.WebView.run_javascript_finish() in a callback function, getting the return (a WebKit2.JavascriptResult objetc), e extrat the value with WebKit2.JavascriptResult.get_value(), I received a "TypeError: Couldn't find foreign struct converter for 'JavaScriptCore.Value'".

I have a "from gi.repository import JavaScriptCore" on the imports, and I dont know why this error is occuring.

ps: Sorry about my terrible english.