ERROR: TypeError: Cannot read properties of undefined (reading ‘indexOf’)

In this code, I have an error that says “Cannot read properties of undefined (reading ‘indexOf’)”

lowPassword(control: FormControl): {
  [lowLevelPassword: string]: boolean;
} {
  if (this.invalidPassword.indexOf(control.value) != -1) {
    return {
      lowLevelPassword: true,
    };
  }
  return null;
}