kit: validation: throw exception if content-type is missing

Describe the bug I get this error since upgrading to SK next-81 (also happens on 83). This possibly happens because of an API route with POST requests like so:

import fetch from 'node-fetch'


/**
 * Load data from API
 */
// Get results from a POST request
export async function post ({ headers, query, body, params, ...rest }) {
    try {
        const res = await fetch(`https://${import.meta.env.VITE_SANITY_ID}.apicdn.sanity.io/v1/data/query/production?query=${encodeURIComponent(body)}`, {
            method: 'GET',
            headers: {
                Authorization: `Bearer ${import.meta.env.VITE_SANITY_TOKEN}`,
            }
        })
        const data = await res.json()

        return {
            status: 200,
            body: data
        }
    }
     catch (error) {
        return {
            status: error.status || 500,
            body: error.message || error.text || `Can't fetch query`
        }
    }
}

Logs

Cannot read property 'split' of undefined
TypeError: Cannot read property 'split' of undefined
    at parse_body (file:///site/node_modules/.pnpm/@sveltejs+kit@1.0.0-next.83_svelte@3.37.0+vite@2.1.5/node_modules/@sveltejs/kit/dist/ssr.js:1330:60)
    at ssr (file:///site/node_modules/.pnpm/@sveltejs+kit@1.0.0-next.83_svelte@3.37.0+vite@2.1.5/node_modules/@sveltejs/kit/dist/ssr.js:1448:9)
    at fetch (file:///site/node_modules/.pnpm/@sveltejs+kit@1.0.0-next.83_svelte@3.37.0+vite@2.1.5/node_modules/@sveltejs/kit/dist/ssr.js:697:30)

Information about your SvelteKit Installation:

  System:
    OS: macOS 11.2.3
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
    Memory: 480.96 MB / 32.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 15.14.0 - /usr/local/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 7.7.6 - /usr/local/bin/npm
  Browsers:
    Brave Browser: 90.1.23.71
    Firefox: 84.0.1
    Safari: 14.0.3
  npmPackages:
    @sveltejs/kit: next => 1.0.0-next.83
    svelte: ^3.37.0 => 3.37.0
    vite: ^2.1.5 => 2.1.5

Severity Well, it kind of blocks the whole app 🙈