code: public static <T> Iterable<T> checkNoNullInside(Iterable<T> argument, String errorMessage) {
          if (argument == null) {
              return argument;
          }
          for (T element : argument) {
              checkNotNull(element, errorMessage);
          }
          return argument;
      }
docs: Tests if the elements inside the argument collection are not null.
  If collection is null or empty the test is ignored.
  
  @param argument     the iterable tested to see if it does not contain null elements; may be null or empty
  @param errorMessage the errorMessage
  @return the argument that was tested.
  @throws java.lang.NullPointerException if argument contains a null element inside