getStaticProps returns undefined when exporting | NextJS

Question

I'm working on a blog with nextjs. I want to export it as a static website. My problem is that I want to make a dynamic routing (for multiple posts) so I created a [post].js file under a blog page (which contains only getStaticProps but works correctly). When building my app, everything is Ok, when running the app (yarn next) everything is also Ok. But when I try to yarn export in order to deploy the website, I get this error :

Error: Error serializing `.title` returned from `getStaticProps` in "/blog/[post]".
Reason: `undefined` cannot be serialized as JSON. Please use `null` or omit this value.
... etc
Error: Export encountered errors on following paths:
        /blog/[post]

I tried to simplify my code as much as possible. All I do is to show the message I pass on props, but even like this, it does not work. All the other components are just esthetical components, so I really don't understand what's the problem. Here's the code of [post].js:

const Post = props => {
    const [enableParticles, setEnableParticles] = React.useState(true);

    return (
        <div className="App">
            <Header blog />
            <Layout>
                <SocialMediaNav />
                <ParticlesNetwork enableParticles={enableParticles} />
                <ToggleButton
                    checked={enableParticles}
                    onClick={() => setEnableParticles(!enableParticles)}
                />
                <SectionWrapper id="blog-homepage" offset={0} minHeight="90vh">
                    {props.title}
                </SectionWrapper>
            </Layout>
            <Footer />
        </div>
    );
};

export async function getStaticPaths() {
    return {
        paths: [
            { params: { post: 'mes_notes_en_probabilites' } }
        ],
        fallback: false,
    };
}

export async function getStaticProps(context) {
    return {
        props: {
            title: context.params.post
        },
    };
}
export default Post;

note: i tried to do as it was said on this tutorial: https://dev.to/akuks/what-is-getstaticpaths-in-nextjs-5ee5

Do you have an idea?