According to section 7.4, page 7-65, if charEncoding is null or empty, it is considered missing. javax.servlet.jsp.JspTagException: java.io.UnsupportedEncodingException: at org.apache.taglibs.standard.tag.common.core.ImportSupport.doEndTag(ImportSupport.java:183)
Already checked for null, but fixed by adding a check for "", to which null would be converted by the EL.