Example code in INotifyPropertyChanged API throws NullReferenceException

[Omcsesz]

Hello, Team!

I searched if this has been reported, but I have not found any issue about this. Anyway I found that the example code in the following site is not working properly:
https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.inotifypropertychanged?view=netframework-4.8

If I create the project, and build it, then click on the Button, I get the following exception:

"System.NullReferenceException: 'Object reference not set to an instance of an object.'
customerList was null."

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Issue Details

---

Hello, Team!

I searched if this has been reported, but I have not found any issue about this. Anyway I found that the example code in the following site is not working properly:
https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.inotifypropertychanged?view=netframework-4.8

If I create the project, and build it, then click on the Button, I get the following exception:

"System.NullReferenceException: 'Object reference not set to an instance of an object.'
customerList was null."

Author:	Omcsesz
Assignees:	-
Labels:	:watch: Not Triaged, Pri3, area-System.ComponentModel
Milestone:	-