Steps to reproduce:

• Install JIRA 5.1.7 and apply a Brazilian Portuguese language pack (haven't tested with other languages)
• Create a JIRA issue as usual and set any due date (you can create more than one for testing purposes – a single issue with settled due date among others is enough to cause the error);
• Install Confluence (tested in 4.3.1 and 4.3.2) and set the application link between them (I used trusted application for it).
• Create a page or blog post in Confluence;
  • Insert a JIRA Macro that returns all issues from a project;
• Save the page and make sure that it is working.
• Now set both the JIRA default language and Index language to Brazilian Portuguese;
• Refresh the JIRA page to make sure that it was correctly applied;
• Refresh the Confluence page (or blog post) and the JIRA Issue Macro no longer retrieves data from JIRA. In the macro it will display the following message:

  "Unable to generate JSON output <br/>class java.io.IOException"
  

  

• Thus, in confluence-application.log, it throws the following error output:

  2012-10-29 15:58:02,750 WARN [http-8090-3] [confluence.extra.jira.JiraIssuesServlet] doGet An IO Exception has been encountered: Unable to generate JSON output
   -- url: /conf432/plugins/servlet/issue-retriever | userName: admin | referer: http://localhost:8090/conf432/display/ds/2012/10/29/test+blog+post+macros
  java.io.IOException: Unable to generate JSON output
  	at com.atlassian.confluence.extra.jira.JsonFlexigridResponseGenerator.generate(JsonFlexigridResponseGenerator.java:344)
  	at com.atlassian.confluence.extra.jira.JiraIssuesServlet.getResult(JiraIssuesServlet.java:210)
  	at com.atlassian.confluence.extra.jira.JiraIssuesServlet.doGet(JiraIssuesServlet.java:120)
  	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
  	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
  	at com.atlassian.plugin.servlet.DelegatingPluginServlet.service(DelegatingPluginServlet.java:42)
  	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
  	at com.atlassian.plugin.servlet.ServletModuleContainerServlet.service(ServletModuleContainerServlet.java:52)
  	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.web.filter.DebugFilter.doFilter(DebugFilter.java:44)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
  	at com.atlassian.labs.botkiller.BotKillerFilter.doFilter(BotKillerFilter.java:36)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
  	at com.atlassian.applinks.core.rest.context.ContextFilter.doFilter(ContextFilter.java:25)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:77)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.security.websudo.MessagesDecoratorFilter.doFilter(MessagesDecoratorFilter.java:59)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.opensymphony.sitemesh.webapp.SiteMeshFilter.obtainContent(SiteMeshFilter.java:129)
  	at com.opensymphony.sitemesh.webapp.SiteMeshFilter.doFilter(SiteMeshFilter.java:77)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:77)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.util.LoggingContextFilter.doFilter(LoggingContextFilter.java:40)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.seraph.filter.SecurityFilter.doFilter(SecurityFilter.java:211)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.security.auth.trustedapps.filter.TrustedApplicationsFilter.doFilter(TrustedApplicationsFilter.java:98)
  	at com.atlassian.confluence.util.AbstractBootstrapHotSwappingFilter.doFilter(AbstractBootstrapHotSwappingFilter.java:30)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.seraph.filter.BaseLoginFilter.doFilter(BaseLoginFilter.java:150)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
  	at com.atlassian.oauth.serviceprovider.internal.servlet.OAuthFilter.doFilter(OAuthFilter.java:70)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:77)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.util.ClusterHeaderFilter.doFilter(ClusterHeaderFilter.java:37)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.johnson.filters.AbstractJohnsonFilter.doFilter(AbstractJohnsonFilter.java:72)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at org.springframework.orm.hibernate.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:170)
  	at com.atlassian.spring.filter.FlushingSpringSessionInViewFilter.doFilterInternal(FlushingSpringSessionInViewFilter.java:29)
  	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.util.ConfluenceErrorFilter.doFilter(ConfluenceErrorFilter.java:22)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:99)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.core.datetime.RequestTimeThreadLocalFilter.doFilter(RequestTimeThreadLocalFilter.java:35)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.gzipfilter.GzipFilter.doFilterInternal(GzipFilter.java:74)
  	at com.atlassian.gzipfilter.GzipFilter.doFilter(GzipFilter.java:51)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.core.filters.cache.AbstractCachingFilter.doFilter(AbstractCachingFilter.java:33)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
  	at com.atlassian.confluence.extra.webdav.servlet.filter.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:43)
  	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
  	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:77)
  	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.web.filter.validateparam.RequestParamValidationFilter.doFilter(RequestParamValidationFilter.java:58)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.web.filter.TranslationModeFilter.doFilter(TranslationModeFilter.java:43)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.plugin.servlet.filter.ActionContextCleanUp.doFilter(ActionContextCleanUp.java:71)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.web.filter.LanguageExtractionFilter.doFilter(LanguageExtractionFilter.java:54)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.util.RequestCacheThreadLocalFilter.doFilter(RequestCacheThreadLocalFilter.java:25)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.web.filter.DebugFilter.doFilter(DebugFilter.java:44)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.core.filters.encoding.AbstractEncodingFilter.doFilter(AbstractEncodingFilter.java:41)
  	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.core.filters.HeaderSanitisingFilter.doFilter(HeaderSanitisingFilter.java:44)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at com.atlassian.confluence.servlet.FourOhFourErrorLoggingFilter.doFilter(FourOhFourErrorLoggingFilter.java:65)
  	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
  	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
  	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
  	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
  	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
  	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
  	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
  	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
  	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
  	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
  	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
  	at java.lang.Thread.run(Thread.java:662)
  Caused by: java.lang.NullPointerException
  	at java.util.Calendar.setTime(Calendar.java:1076)
  	at java.text.SimpleDateFormat.format(SimpleDateFormat.java:875)
  	at java.text.SimpleDateFormat.format(SimpleDateFormat.java:868)
  	at java.text.DateFormat.format(DateFormat.java:316)
  	at com.atlassian.confluence.extra.jira.JsonFlexigridResponseGenerator.appendDueDate(JsonFlexigridResponseGenerator.java:232)
  	at com.atlassian.confluence.extra.jira.JsonFlexigridResponseGenerator.getElementJson(JsonFlexigridResponseGenerator.java:160)
  	at com.atlassian.confluence.extra.jira.JsonFlexigridResponseGenerator.getOutputAsString(JsonFlexigridResponseGenerator.java:320)
  	at com.atlassian.confluence.extra.jira.JsonFlexigridResponseGenerator.generate(JsonFlexigridResponseGenerator.java:340)
  	... 143 more
  

Workaround 1:

• Remove the due date from all the issues; The JIRA Issue Macro will start working again;

Workaround 2:

• Set the JIRA language to English once again; The JIRA Issue Macro will start working again.