in src/app/rule/rule.component.ts [105:111]
addDomainRangeValue() {
const control = new FormControl('');
const domainArray = <FormArray> this.formGroup.controls.domain;
const rangeArray = <FormArray> this.formGroup.controls.range;
domainArray.push(new FormControl(''));
rangeArray.push(new FormControl(''));
}