TypeScript null detection obscurity

Even though control.parent is checked for having a value, it is still
flagged as potentially null. Fixed by capturing the variable separately
so TS detects it as having a value within the closure.

angular-reactive-validation/src/get-control-path.ts

@@ -3,18 +3,19 @@ import { AbstractControl } from '@angular/forms';
 /**
  * Given a control, returns a string representation of the property path to
  * this control. Thus, for a FormControl 'firstName', that is part of a
- * FormGroup references to as 'name', this function will return: 'name.firstName'.
+ * FormGroup named 'name', this function will return: 'name.firstName'.
  *
  * Note that FormArray indexes are also put in the path, e.g.: 'person.0.name.firstName'.
  */
 export function getControlPath(control: AbstractControl): string {
- if (control.parent) {
- let path = getControlPath(control.parent);
+ const parentControl = control.parent;
+ if (parentControl) {
+ let path = getControlPath(parentControl);
  if (path) {
  path += '.';
  }
- return path + Object.keys(control.parent.controls).find(key => {
- const controls = control.parent.controls;
+ return path + Object.keys(parentControl.controls).find(key => {
+ const controls = parentControl.controls;
  if (Array.isArray(controls)) {
  return controls[Number(key)] === control;
  } else {