anchor.diff:     * function is returned.
      * If [orElse] is omitted, it defaults to throwing a [StateError].
      */
  -  E firstWhere(bool test(E element), { E orElse() }) {
  +  E firstWhere(bool test(E element), {E orElse()}) {
       for (E element in this) {
         if (test(element)) return element;
       }
  
positive.code:     }
      return false;
    }
  
  
    /**
     * Applies the function [f] to each element of this collection in iteration
  
negative.code:    */
    bool get isNotEmpty => !isEmpty;
  
    /**
     * Returns a lazy iterable of the [count] first elements of this iterable.
     *
     * The returned `Iterable` may contain fewer than `count` elements, if `this`
  