code: public String getJobParameter(String key, String defaultValue) {
  		final GlobalJobParameters conf = context.getExecutionConfig().getGlobalJobParameters();
  		if (conf != null && conf.toMap().containsKey(key)) {
  			return conf.toMap().get(key);
  		} else {
  			return defaultValue;
  		}
  	}
docs: Gets the global job parameter value associated with the given key as a string.
  
  @param key          key pointing to the associated value
  @param defaultValue default value which is returned in case global job parameter is null
  or there is no value associated with the given key
  @return (default) value associated with the given key