java.io.UnsupportedEncodingException: UTF-8;

I'm trying to setup my web application with a component for scanning documents on the browser, and this particular component has a javascript code that submits the scanned document using multipart, and has a servlet that handles the submitted form. Part of the the javascript code that submits the scanned document is the following:

a.xhr.setRequestHeader("Content-Type","multipart/form-data; boundary="+a.boundaryString)

The Content-Type header of the associated POST is:

Content-Type:"multipart/form-data; charset=UTF-8; boundary=AaBbCc=_X30"

Once the Servlet that handles the submit goes through the doPost method, I get the following stacktrace:

14:31:46,448 ERROR [io.undertow.request] (default task-60) UT005023: Exception handling request to /scan/AtalasoftCaptureHandler: java.lang.RuntimeException: java.io.UnsupportedEncodingException: UTF-8;
at io.undertow.servlet.spec.HttpServletRequestImpl.parseFormData(HttpServletRequestImpl.java:755)
at io.undertow.servlet.spec.HttpServletRequestImpl.getParameter(HttpServletRequestImpl.java:627)
at javax.servlet.ServletRequestWrapper.getParameter(ServletRequestWrapper.java:194)
at javax.servlet.ServletRequestWrapper.getParameter(ServletRequestWrapper.java:194)
at javax.servlet.ServletRequestWrapper.getParameter(ServletRequestWrapper.java:194)
at com.atalasoft.imaging.webcontrols.capture.WebCaptureRequestHandler.processRequest(Unknown Source)
at com.atalasoft.imaging.webcontrols.capture.WebCaptureRequestHandler.doPost(Unknown Source)
at ScanHandler.doPost(ScanHandler.java:44)
Caused by: java.io.UnsupportedEncodingException: UTF-8;
at java.lang.StringCoding.decode(StringCoding.java:190)
at java.lang.String.<init>(String.java:414)
at java.lang.String.<init>(String.java:479)
at io.undertow.util.MultipartParser$ParseState.headerName(MultipartParser.java:174)
at io.undertow.util.MultipartParser$ParseState.parse(MultipartParser.java:107)
at io.undertow.server.handlers.form.MultiPartParserDefinition$MultiPartUploadHandler.parseBlocking(MultiPartParserDefinition.java:206)
at io.undertow.servlet.spec.HttpServletRequestImpl.parseFormData(HttpServletRequestImpl.java:753)
... 85 more

Looks like the HttpServerExchange.extractCharset method is considering the semicolon as part of the charset, and then it considers the encoding invalid.