[error record] the parameter 'can't have a value of' null 'because of its type, but the im

One 、 Error message

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Opened one written last year Flutter project , Find a direct error ;

The parameter 'icon' can't have a value of 'null' because of its type, but the implicit default value is 'null'. (Documentation)  Try adding either an explicit non-'null' default value or the 'required' modifier.

Two 、 Solution

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This is because Flutter SDK Version update , The examination of grammar has become more strict , During compilation, null judgment is added to the class in the construction method ;

stay Dart When a member variable of a class is defined , Add... After type ? Symbol , Declare it as nullable type , And Kotlin similar , After modification , Compile no more errors ;

class CommonModel { 
      final String? icon;  final String? title;  final String? url;  final String? statusBarColor;  final bool? hideAppBar;  CommonModel({ 
    this.icon, this.title, this.url, this.statusBarColor, this.hideAppBar});}