Cannot read properties of undefined error when using array notation in expressionProperties

[andyault]

Description
When trying to use an expressionProperty to update an array item, an error is thrown when using array syntax (array[i]), but not when using dot syntax (array.i).

Minimal Reproduction
https://stackblitz.com/edit/angular-q2hju2-evvvg2?file=src/app/app.component.ts

If line 26 in src/app/app.component.ts is uncommented, the console will show an error:

ERROR TypeError: [Formly Error] [Expression "templateOptions.options[1].label"] Cannot read properties of undefined (reading '1')
    at FieldExpressionExtension.setExprValue (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:3177:40)
    at FieldExpressionExtension.checkFieldExpressionChange (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:3021:30)
    at eval (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:2976:27)
    at Array.forEach (<anonymous>)
    at FieldExpressionExtension._checkField (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:2969:34)
    at FieldExpressionExtension.checkField (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:2932:41)
    at Object.eval [as _checkField] (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:2758:31)
    at FormlyFormBuilder.buildForm (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:828:31)
    at FormlyForm.ngOnChanges (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@ngx-formly/core@5.12.0/bundles/ngx-formly-core.umd.js:1311:40)
    at checkAndUpdateDirectiveInline (angular-q2hju2-evvvg2.stackblitz.io/turbo_modules/@angular/core@7.2.16/bundles/core.umd.js:22116:23)

Your Environment

• Angular version: 13.2.2
• Formly version: 5.12.0

Additional context
Looks like this issue was previously reported (and fixed) here.

[aitboudad]

This issue has been fixed and released as part of v5.12.1 release.

Please let us know, in case you are still encountering a similar issue/problem.
Thank you!