When I was coding in Flutter on Android Studio Chipmunk 2021.2.1, a new windows of server's certificate is not trusted appeared, I didn't know what to do, I thought that was a kind of attack so I declined the certificate. But know, after closing and reopening the app, when I build it, nothing more screen in the Chrome(web) built environment with a error that I think was already there before when the app was screening good (I am in unsound null safety mode). This is the error :

Error: Unexpected null value.
    at Object.throw_ [as throw] (http://localhost:65099/dart_sdk.js:5405:11)
    at Object.nullCheck (http://localhost:65099/dart_sdk.js:5732:30)
    at get user (http://localhost:65099/packages/epressing/profile_folder/profile_edit_page.dart.lib.js:1252:19)
    at desc.get [as user] (http://localhost:65099/dart_sdk.js:5906:17)
    at get myUser (http://localhost:65099/packages/epressing/profile_folder/profile_edit_page.dart.lib.js:1222:73)
    at desc.get [as myUser] (http://localhost:65099/dart_sdk.js:5906:17)
    at new main.MyApp.new (http://localhost:65099/packages/epressing/auth_folder/login_widget.dart.lib.js:1078:48)
    at main$ (http://localhost:65099/packages/epressing/auth_folder/login_widget.dart.lib.js:1119:22)
    at main$.next (<anonymous>)
    at http://localhost:65099/dart_sdk.js:43063:33
    at _RootZone.runUnary (http://localhost:65099/dart_sdk.js:42919:58)
    at _FutureListener.thenAwait.handleValue (http://localhost:65099/dart_sdk.js:37493:29)
    at handleValueCallback (http://localhost:65099/dart_sdk.js:38088:49)
    at _Future._propagateToListeners (http://localhost:65099/dart_sdk.js:38126:17)
    at [_completeWithValue] (http://localhost:65099/dart_sdk.js:37955:23)
    at http://localhost:65099/dart_sdk.js:37112:46
    at _RootZone.runUnary (http://localhost:65099/dart_sdk.js:42919:58)
    at _FutureListener.then.handleValue (http://localhost:65099/dart_sdk.js:37493:29)
    at handleValueCallback (http://localhost:65099/dart_sdk.js:38088:49)
    at _Future._propagateToListeners (http://localhost:65099/dart_sdk.js:38126:17)
    at [_completeWithValue] (http://localhost:65099/dart_sdk.js:37955:23)
    at async._AsyncCallbackEntry.new.callback (http://localhost:65099/dart_sdk.js:37991:35)
    at Object._microtaskLoop (http://localhost:65099/dart_sdk.js:43223:13)
    at _startMicrotaskLoop (http://localhost:65099/dart_sdk.js:43229:13)
    at http://localhost:65099/dart_sdk.js:38359:9

When I try to build it with Edge(web) built, that print out another the same error. With Windows(desktop) too they say :

Exception: No Windows desktop project configured. See https://docs.flutter.dev/desktop#add-desktop-support-to-an-existing-flutter-app to learn about adding Windows support to a project.

(my computer hardly run with android emulator, so I don't use that).

I've tried to download two kind of google server's certificate on internet (which is in apk type) and add them, but that didn't appeared in the little windows of choosing files or folder certificate path in the

Files > Setting > Tools > Server Certificate > Add

How can i proceed to add a server certificate if that is the problem and necessary, or how can i solve my problem ?