code: private String addProperty(String key) {
  
          if (System.getProperty(key) != null) {
              m_configuration.put(key, System.getProperty(key));
          }
          return m_configuration.get(key);
      }
docs: Adds and returns the property for the given key.<p>
  
  @param key the key to add the property
  
  @return the value of that property