code: public static void openUserCode(Function stub, Configuration parameters) throws Exception {
  		try {
  			FunctionUtils.openFunction(stub, parameters);
  		} catch (Throwable t) {
  			throw new Exception("The user defined 'open(Configuration)' method in " + stub.getClass().toString() + " caused an exception: " + t.getMessage(), t);
  		}
  	}
docs: Opens the given stub using its {@link org.apache.flink.api.common.functions.RichFunction#open(Configuration)} method. If the open call produces
  an exception, a new exception with a standard error message is created, using the encountered exception
  as its cause.
  
  @param stub The user code instance to be opened.
  @param parameters The parameters supplied to the user code.
  
  @throws Exception Thrown, if the user code's open method produces an exception.