code: @Nonnull
    public ValidationResultList executeValidation (@Nonnull final IValidationSource aSource)
    {
      return executeValidation (aSource, (Locale) null);
    }
docs: Perform a validation with all the contained executors and the system
  default locale.
  
  @param aSource
  The source artefact to be validated. May not be <code>null</code>.
  contained executor a result is added to the result list.
  @return The validation result list. Never <code>null</code>. For each
  contained executor a result is added to the result list.
  @see #executeValidation(IValidationSource, ValidationResultList, Locale)
  @since 5.1.1