code: @Nonnegative
    public int getAllCount (@Nullable final Predicate <? super IError> aFilter)
    {
      int ret = 0;
      for (final ValidationResult aItem : this)
        ret += aItem.getErrorList ().getCount (aFilter);
      return ret;
    }
docs: Count all items according to the provided filter.
  
  @param aFilter
  Optional filter to use. May be <code>null</code>.
  @return The number of errors matching the provided filter.