code: public String getString(@NotNull final String key, @Nullable final String defaultValue) {
          return System.getProperty(key, props.getProperty(key, defaultValue));
      }
docs: Returns a value from the properties file. If the value was specified as a
  system property or passed in via the -Dprop=value argument - this method
  will return the value from the system properties before the values in the
  contained configuration file.
  
  @param key the key to lookup within the properties file
  @param defaultValue the default value for the requested property
  @return the property from the properties file