Link unfurling fails because of missing conversationType

I implemented the link unfurling example code in my project.
This works for unfurling links pasted in chats, but when I call the sharing feature from @microsoft/teams-js it breaks.

sharing.shareWebContent({
    content: [{
        url: sharingUrl,
        type: 'URL',
        message: `Take a look at this item`,
        preview: true,
    }]
});

This should show a unfurled preview like so:

But that doesn't work because in the request payload sent to the bot the Conversation.ConversationType is missing.
But in a chat the ConversationType is "groupChat" and it works.

JSON deserialization for type 'Microsoft.Teams.Api.Conversation' was missing required properties including: 'conversationType'.

Start by reproducing the sharing.shareWebContent request and inspect the bot payload's Microsoft.Teams.Api.Conversation deserialization. Compare it with the working chat payload, focusing on the missing ConversationType property. Done means shared links produce an unfurled preview without the required-property deserialization error.