Exceção ao adicionar biblioteca de tags personalizadas ao JSP

Eu tenho o mesmo problema que esta pergunta sem resposta de quase 2 anos atrás.

<%@ taglib uri="/WEB-INF/tlds/myLib" prefix="myLib" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

Eu tenho essas duas linhas no meu JSP. Originalmente, eu estava usando apenas a biblioteca principal JSTL e tudo funcionou bem. Assim que adiciono uma biblioteca personalizada, recebo uma exceção como esta:

java.lang.NullPointerException
at org.apache.jasper.compiler.TagLibraryInfoImpl.toString(TagLibraryInfoImpl.java:129)
at java.lang.String.valueOf(String.java:2979)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at java.util.concurrent.ConcurrentHashMap.toString(ConcurrentHashMap.java:1321)
at org.apache.taglibs.standard.tag.common.core.OutSupport.out(OutSupport.java:211)
at org.apache.taglibs.standard.tag.common.core.OutSupport.doStartTag(OutSupport.java:132)
at org.apache.jsp.FormTest_jsp._jspx_meth_c_out_3(FormTest_jsp.java:306)
at org.apache.jsp.FormTest_jsp._jspx_meth_c_forEach_1(FormTest_jsp.java:256)
at org.apache.jsp.FormTest_jsp._jspService(FormTest_jsp.java:83)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:411)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:875)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:739)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:575)
at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:546)
at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:428)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:378)
at form.FormServlet.processRequest(FormServlet.java:60)
at form.FormServlet.doPost(FormServlet.java:89)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:415)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:201)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:565)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
at java.lang.Thread.run(Thread.java:745)

Se eu remover qualquer uma das duas diretivas taglib, tudo funcionará corretamente.

<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.1" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd">
  <tlib-version>1.0</tlib-version>
  <short-name>mylib</short-name>
  <uri>/WEB-INF/tlds/myLib</uri>
  <tag>
    <name>beaner</name>
    <tagclass>form.BeanTagHandler</tagclass>
    <bodycontent>empty</bodycontent>
  </tag>
</taglib>

tld é mínimo para tentar fazer isso funcionar.

Agradeceria se alguém pudesse oferecer algumas dicas sobre qual pode ser o problema. Obrigado.

EDIT: Encontrada a origem do problema.

<table>
<tr>
<th>Attribute Name</th>
<th>Attribute Value</th></tr>
<c:forEach var="a" items="${applicationScope}">
<tr>
<td> <c:out value="${a.key}"/> </td>
<td> <c:out value="${a.value}" /> </td>
</tr>
</c:forEach>
</table>

A parte problemática é o c: out de $ {a.value}. O jsp funciona bem sem ele. Por algum motivo, funciona bem quando não importo minha biblioteca de tags personalizadas. Alguma idéia de por que tentar eliminar os valores do applicationScope causaria problemas?