웹 페이지 만들기 시 오류

유튜브 페이지를 연결한 간단한 웹 페이지를 만들려고
웹 페이지 만들기에서 아래와 같은 소스를 템플릿 소스에 넣었습니다.

템플릿 HTML만 남기고 나머지 항목은 모두 지웠습니다.

<!DOCTYPE html>
<HTML>
 <HEAD></HEAD>
 <BODY>
     <iframe width="640" height="360" src="https://www.youtube.com/embed/~~~" frameborder="0" allowfullscreen></iframe>
 </BODY>
</HTML>

해당 코드 입력 후 미리 보기로 확인해보니 아래와 같은 오류가 나와서요.
어떤 부분에 잘못이 있는지 문의드려요.

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
    at java.lang.String.substring(Unknown Source)
    at com.threerabbitz.book.page.C.a(SourceFile:31)
    at com.threerabbitz.book.controller.WebPageController.a(SourceFile:68)
    at com.threerabbitz.book.controller.WebPageController.load(SourceFile:42)
    at sun.reflect.GeneratedMethodAccessor146.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.threerabbitz.base.i.b(SourceFile:40)
    at com.threerabbitz.base.j.a(SourceFile:53)
    at com.threerabbitz.base.FrontFilter.doFilter(SourceFile:94)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

다음과 같이 태그를 소문자로 써주세요.

<!DOCTYPE html>
<html>
 <head></head>
 <body>
     <iframe width="640" height="360" src="https://www.youtube.com/embed/~~~" frameborder="0" allowfullscreen></iframe>
 </body>
</html>

다음 릴리즈에서 에러 메시지를 개선하도록 하겠습니다.

아~ 이런 팁이 감사합니다. ^^