Task: Double-check post update logic

Pay attention to this:

      const updatedPost = await ctx.prisma.post.update({
        where: { id: args.where.id },
        data: {
          ...args.data,
          ...sharedFields,

At the very least, the issue here is that sharedFields, which are taken from the old topic, overwrite the submitted data, at least regarding the image.

But generally speaking, we need to re-check all the logic from the frontend because react-hook-form cannot set fields to null on update and might just overwrite them with an empty string.