code: public Map<ExecutionProperty, List<String>> parseProperties(Map<ExecutionProperty, List<String>> propertyMap, String... args) {
          for ( ExecutionProperty p : getProperties()) {
             String value = System.getProperty(p.getSystemProperty());
             if ( value != null ) {
                 addValues(propertyMap, p, value);
             }
          }
          return propertyMap;
      }
docs: Add to the provided propertyMap any properties available from this source
  
  Where the map already contains property values under a given key, extra property values should be
  appended to the List
  
  @return propertyMap, with parsed properties added