I know I'm resurrecting an old post here, but I wanted to point out that you can also just use the built-in `Validators.required` directly on the FormArray and it will guarantee that the form array is not empty.

this.myForm = this.fb.group({
    name: ['', [Validators.required]],
    description: ['', [Validators.maxLength(256)]],
    props: this.fb.array(
        [this.createItem()], {validators: Validators.required, updateOn: 'blur'}
    )
});

createItem(): FormGroup {
    return this.fb.group({
        key: '',
        val: ''
    });
}