chore(client-fetch,client-nuxt): updates getValidRequestBody to return undefined by default

Author: Fransis Young

packages/openapi-ts/src/plugins/@hey-api/client-fetch/bundle/client.ts

@@ -226,7 +226,8 @@ export const createClient = (config: Config = {}): Client => {
       return options.body;
     }
 
-    return null;
+    // no body was provided
+    return undefined;
   }
 
   const makeMethodFn =

packages/openapi-ts/src/plugins/@hey-api/client-next/bundle/client.ts

@@ -214,7 +214,8 @@ export const createClient = (config: Config = {}): Client => {
       return options.body;
     }
 
-    return null;
+    // no body was provided
+    return undefined;
   }
 
   const makeMethodFn =