precachePicture throwing null exception when using in main.dart

Question

I am using svg in my onboarding screen and I want to precache it as it takes time for svg to load. But whenever I am trying to precache, I'm getting an exception.

    ════════ Exception caught by SVG ═══════════════════════════════════════════════
    The following _CastError was thrown resolving a single-frame picture stream:
    Null check operator used on a null value

My main.dart code:

    Future.wait(
      [
        precachePicture(
          ExactAssetPicture(
              SvgPicture.svgStringDecoderBuilder, 'assets/shopping.svg'),
          null,
        ),
      ],
    );
    runApp(
      MaterialApp(
        initialRoute: "welcome_screen",
        debugShowCheckedModeBanner: false,
        routes: {
          "signup": (context) => const SignUp(),
          "signin": (context) => const SignIn(),
          "welcome_screen": (context) => const WelcomeScreen(),
        },
      ),
    );

I want to use the svg on WelcomeScreen().