set rawBody to null when body is nullish in simulated load fetch (sveltejs#2294)

Author: Conduitry

packages/kit/src/runtime/server/page/load_node.js

@@ -151,7 +151,10 @@ export async function load_node({
 							method: opts.method || 'GET',
 							headers,
 							path: relative,
-							rawBody: new TextEncoder().encode(/** @type {string} */ (opts.body)),
+							rawBody:
+								opts.body == null
+									? null
+									: new TextEncoder().encode(/** @type {string} */ (opts.body)),
 							query: new URLSearchParams(search)
 						},
 						options,