If we’re following how mat-select works, these changes should apply only in multiple mode. In single-selection mode null options act as a reset.

Why only in multiple mode? Can we handle both? Like maybe setting the value to null is a "reset" in both select and button toggle unless there's an option inside that binds to null. Then select that.

My use case is that I have a record that's either deemed a Failure, Not a Failure, Or not yet reviewed. I'm storing this in the database just using a nullable boolean. The following code doesn't select "Pending" when you load it up for the first time because of this "null means reset" philosophy

<mat-button-toggle-group color="primary" [(ngModel)]="row.failure">
  <mat-button-toggle [value]="null">Pending Review</mat-button-toggle>
  <mat-button-toggle [value]="false">Incident</mat-button-toggle>
  <mat-button-toggle [value]="true">Failure</mat-button-toggle>
</mat-button-toggle-group>

Sounds like the same code wouldn't work if I changed it to a mat-select instead of using button-toggle. I can work around this easily but it's kind of odd that you can't treat null as a real value, especially when we have undefined as an option in JS which seems more like a "reset" style of value.