FormArray TypeError: value.forEach is not a function

The setValue method takes simple values:

   this.techFormArray = new FormArray([
        new FormControl(''),
        new FormControl(''),
        new FormControl('')
    ]);

    this.jobDetails = this.formBuilder.group({
        techs: this.techFormArray
    });

    this.jobDetails.setValue({
      techs: ['a', 'b', 'c']
    });