Replace a workaround with a more semantic one. - In old implementation, it has not clear intention in the syntax. - I move the line doing real works into the try-except block to emphasize the intention of skipping scene nodes that is incomplete.

package org.madbutterfly;

import java.lang.Exception;

public class InvalidStateException extends Exception {
    public InvalidStateException() {
	super();
    }
    public InvalidStateException(String msg) {
	super(msg);
    }
}