Cannot create property 'validator' on string

I had a same issue and I was passing form object as a value like formGroup="form" but you need to bind the form object using [] aroung as [formGroup]="form".

See the example below:

<form [formGroup]="form">
    // form-controls
</form>

You're passing the form group name as a string rather than a reference to the formGroup and trying to typecast it as a FormGroup (group="addressFormGroup"). group="addressFormGroup" doesn't pass the formGroup object, it passes a string with the value of addressFormGroup.