fix(ios): network log empty response body

Author: ahmedAlaaInstabug

test/utils/XhrNetworkInterceptor.spec.ts

@@ -236,7 +236,7 @@ describe('Network Interceptor', () => {
         expect.objectContaining({
           errorDomain: 'ClientError',
           errorCode: 0,
-          responseBody: null,
+          responseBody: '',
         }),
       );
     });