bug(CdkListbox): cdkListboxValue should allow undefined for initial value

[shhdharmen]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

Currently, cdkListboxValue does not allow any other value than what is given as value for cdkOptions. This is fine as it prevents from selecting invalid value.

But, it should also allow undefined so that initial state of listbox works fine without needing to have a selected value.

Reproduction

StackBlitz link: https://stackblitz.com/edit/ofsskkdf?file=src%2Fexample%2Fcdk-listbox-value-binding-example.ts

Observe that Angular Compiler is giving error:

✘ [ERROR] TS2322: Type 'string[] | undefined' is not assignable to type 'readonly string[]'.
  Type 'undefined' is not assignable to type 'readonly string[]'. [plugin angular-compiler]

    src/example/cdk-listbox-value-binding-example.html:7:7:
      7 │       [cdkListboxValue]="starter"
        ╵        ~~~~~~~~~~~~~~~

  Error occurs in the template of component CdkListboxValueBindingExample.

    src/example/cdk-listbox-value-binding-example.ts:9:15:
      9 │   templateUrl: 'cdk-listbox-value-binding-example.html',
        ╵                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


✘ [ERROR] TS4104: The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type 'string[]'. [plugin angular-compiler]

    src/example/cdk-listbox-value-binding-example.html:8:31:
      8 │       (cdkListboxValueChange)="starter = $event.value"
        ╵                                ~~~~~~~~~~~~~~~~~~~~~~

  Error occurs in the template of component CdkListboxValueBindingExample.

    src/example/cdk-listbox-value-binding-example.ts:9:15:
      9 │   templateUrl: 'cdk-listbox-value-binding-example.html',
        ╵                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Expected Behavior

cdkListboxValue should allow undefined to handle initial state.

Actual Behavior

cdkListboxValue does not allow any other type of values except what is given as value in its cdkOptions.

Environment

• Angular: 20.1.0
• CDK/Material: 20.1.0
• Browser(s): Chrome
• Operating System (e.g. Windows, macOS, Ubuntu): macOS

[crisbeto]

My understanding is that resetting would be done by assigning an empty array.