code: public void assertIsPositiveIfPresent(Integer integer, String propertyName) {
          if (integer != null && integer <= 0) {
              problemReporter.report(new Problem(this, String.format("%s must be positive", propertyName)));
          }
      }
docs: Asserts the integer is either null or positive, reporting to {@link ProblemReporter} with this context if it is.
  
  @param integer      Value to assert on.
  @param propertyName Name of property.