flutter报错 -- The argument type ‘Function‘ can‘t be assigned to the parameter type ‘void Function?‘

flutter报错信息：

The argument type ‘Function’ can’t be assigned to the parameter type ‘void Function()?’

参数类型“Function”不能被赋值给参数类型“void Function()?”

声明函数方法改为：
Function dataDelete; //报错
final void Function() dataDelete; //改成这个，不报错