snapshot.data["additional_text"] is Null

[alessioC42]

java.lang.Exception: type 'Null' is not a subtype of type 'String'

#0      _UploadScreenState.build.<anonymous closure> (package:sph_plan/view/mein_unterricht/upload_page.dart:453)
#1      _FutureBuilderState.build (package:flutter/src/widgets/async.dart:609)
#2      StatefulElement.build (package:flutter/src/widgets/framework.dart:5583)
#3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:5471)
#4      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:5634)
#5      Element.rebuild (package:flutter/src/widgets/framework.dart:5187)
#6      BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2895)
#7      WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:984)
#8      RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:457)
#9      SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1325)
#10     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1255)
#11     SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1113)
#12     _rootRun (dart:async/zone.dart:1399)
#13     _CustomZone.run (dart:async/zone.dart:1301)
#14     _CustomZone.runGuarded (dart:async/zone.dart:1209)
#15     _invoke (dart:ui/hooks.dart:314)
#16     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:383)
#17     _drawFrame (dart:ui/hooks.dart:283)

at ly.count.dart.countly_flutter.CountlyFlutterPlugin.onMethodCall(Unknown Source:742)
at c4.k$a.a(Unknown Source:17)
at p3.c.l(Unknown Source:18)
at p3.c.m(Unknown Source:40)
at p3.c.i(Unknown Source:0)
at p3.b.run(Unknown Source:12)
at android.os.Handler.handleCallback(Handler.java:907)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:216)
at android.app.ActivityThread.main(ActivityThread.java:7625)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)