WebLogic: NullPointerException in HstLinkTag when handling request without specific encoding

When the character encoding is not set for a request the HstLinkTag throws an nullpointer exception. The default encoding should be used when not specified.
Workaround is to globally configure the encoding in the container so all requests set the encoding.

<May 28, 2014 4:38:36 PM CEST> <Error> <HTTP> <BEA-101107> <[ServletContext@840011536[app:hippogogreen-enterprise-3.09.02-SNAPSHOT module:/site path:null spec-version:3.0]] Problem occurred while serving the error page.
java.lang.NullPointerException: charsetName
at java.net.URLEncoder.encode(URLEncoder.java:210)
at org.hippoecm.hst.tag.HstLinkTag.getQueryString(HstLinkTag.java:328)
at org.hippoecm.hst.tag.HstLinkTag.doEndTag(HstLinkTag.java:182)
at jsp_servlet.web_45_inf._jsp._login.login_failure._jspService(_login_failure.java:121)
at weblogic.servlet.jsp.JspBase.service(JspBase.java:34)
Truncated. see log file for complete stacktrace
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