code: public void assertNotEmpty(Collection<?> collection, String propertyName) {
          if (CollectionUtils.isNullOrEmpty(collection)) {
              problemReporter.report(new Problem(this, String.format("%s requires one or more items", propertyName)));
          }
      }
docs: Asserts the collection is not null and not empty, reporting to {@link ProblemReporter} with this context if it is.
  
  @param collection   Collection to assert on.
  @param propertyName Name of property.