NPE on custom field deletion

[ERROR] ServletDispatcher - Could not execute action <java.lang.NullPointerException>java.lang.NullPointerException
        at com.atlassian.jira.issue.cache.DefaultCacheManager.flushChildren(DefaultCacheManager.java:96)
        at com.atlassian.jira.issue.managers.DefaultCustomFieldManager.removeCustomField(DefaultCustomFieldManager.java:381)
        at com.atlassian.jira.web.action.admin.customfields.DeleteCustomField.doExecute(DeleteCustomField.java:34)
        at webwork.action.ActionSupport.execute(ActionSupport.java:153)
        at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:54)
        at webwork.dispatcher.GenericDispatcher.executeAction(GenericDispatcher.java:132)
        at com.atlassian.jira.web.dispatcher.JiraServletDispatcher.service(JiraServletDispatcher.java:209)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at com.atlassian.jira.web.filters.AccessLogFilter.doFilter(AccessLogFilter.java:73)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:119)