[fix] set rawBody to null when body is nullish in simulated load fetch (#2295)

Author: Conduitry

.changeset/polite-donkeys-learn.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+avoid setting rawBody/body to an empty Uint8Array when a load's fetch function is called with no body during SSR

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

@@ -151,7 +151,7 @@ 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(opts.body),
 							query: new URLSearchParams(search)
 						},
 						options,