code: public void execute( EnforcerRuleHelper helper )
          throws EnforcerRuleException
      {
          Object propValue = resolveValue( helper );
  
          // Check that the property is not null or empty string
          if ( propValue == null )
          {
              String message = getMessage();
              if ( message == null )
              {
                  message = getName() + " \"" + getPropertyName() + "\" is required for this build.";
              }
              throw new EnforcerRuleException( message );
          }
          // If there is a regex, check that the property matches it
          if ( regex != null && !propValue.toString().matches( regex ) )
          {
              if ( regexMessage == null )
              {
                  regexMessage = getName() + " \"" + getPropertyName() + "\" evaluates to \"" + propValue + "\".  "
                      + "This does not match the regular expression \"" + regex + "\"";
              }
              throw new EnforcerRuleException( regexMessage );
          }
      }
docs: Execute the rule.
  
  @param helper the helper
  @throws EnforcerRuleException the enforcer rule exception