Project lead user can be deleted, causing errors in log

If a user is set as the Lead of a project or component, the user should not be deletable until they are removed from these roles. Currently they can be deleted, resulting in this error if a project lead is deleted:

2005-01-18 17:29:29,072 ERROR [jira.action.component.ComponentUtils] com.opensymphony.user.EntityNotFoundException: No user bob found
com.opensymphony.user.EntityNotFoundException: No user bob found
at com.opensymphony.user.UserManager.getEntity(UserManager.java:302)
at com.opensymphony.user.UserManager.getUser(UserManager.java:193)
at com.atlassian.jira.action.component.ComponentUtils.isUserAssignable(ComponentUtils.java:137)
at com.atlassian.jira.action.component.ComponentUtils.isProjectLeadAssignable(ComponentUtils.java:48)
at com.atlassian.jira.web.action.project.ViewProjects.isDefaultAssigneeAssignable(ViewProjects.java:75)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at webwork.util.ValueStack.findValue(ValueStack.java:429)
at webwork.util.SimpleTest.test(SimpleTest.java:391)
at webwork.util.ValueStack.test(ValueStack.java:131)
at webwork.view.taglib.IfTag.doStartTag(IfTag.java:38)
at secure._project._views._viewprojectsjsp._jspService(_viewprojects_jsp.java:345)
at com.caucho.jsp.JavaPage.service(JavaPage.java:75)

and this error if a component lead is deleted:

2005-01-18 17:13:18,485 ERROR [web.action.project.ViewProject] Could not retrieve full name for user: bob
com.opensymphony.user.EntityNotFoundException: No user bob found
at com.opensymphony.user.UserManager.getEntity(UserManager.java:302)
at com.opensymphony.user.UserManager.getUser(UserManager.java:193)
at com.atlassian.jira.web.action.JiraWebActionSupport.getUserFullName(JiraWebActionSupport.java:219)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at webwork.util.ValueStack.findValue(ValueStack.java:429)
at webwork.util.ValueStack.findValue(ValueStack.java:171)
at webwork.view.taglib.WebWorkBodyTagSupport.findValue(WebWorkBodyTagSupport.java:60)
at webwork.view.taglib.BasicPropertyTag.doStartTag(BasicPropertyTag.java:55)
at includes._panels._project._componentsjsp._jspService(_components_jsp.java:224)
at com.caucho.jsp.JavaPage.service(JavaPage.java:75)
at com.caucho.jsp.Page.subservice(Page.java:497)
at com.caucho.server.http.FilterChainPage.doFilter(FilterChainPage.java:182)
at com.caucho.server.http.Invocation.service(Invocation.java:315)
at com.caucho.server.http.CacheInvocation.service(CacheInvocation.java:135)
at com.caucho.server.http.QRequestDispatcher.include(QRequestDispatcher.java:369)
at com.caucho.server.http.QRequestDispatcher.include(QRequestDispatcher.java:276)
at com.caucho.jsp.QPageContext.include(QPageContext.java:538)
at secure._project._views._viewprojectjsp._jspService(_viewproject_jsp.java:457)
at com.caucho.jsp.JavaPage.service(JavaPage.java:75)
at com.caucho.jsp.Page.subservice(Page.java:497)
at com.caucho.server.http.FilterChainPage.doFilter(FilterChainPage.java:182)
at com.caucho.server.http.Invocation.service(Invocation.java:315)
at com.caucho.server.http.CacheInvocation.service(CacheInvocation.java:115)
at com.caucho.server.http.QRequestDispatcher.forward(QRequestDispatcher.java:225)
at com.caucho.server.http.QRequestDispatcher.forward(QRequestDispatcher.java:106)
at com.caucho.server.http.QRequestDispatcher.forward(QRequestDispatcher.java:83)
at com.atlassian.jira.web.dispatcher.JiraServletDispatcher.service(JiraServletDispatcher.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.caucho.server.http.FilterChainServlet.doFilter(FilterChainServlet.java:96)
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:142)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:58)
at com.atlassian.jira.web.filters.SitemeshExcludePathFilter.doFilter(SitemeshExcludePathFilter.java:36)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.seraph.filter.SecurityFilter.doFilter(SecurityFilter.java:167)

No doubt this causes other exceptions elsewhere in the UI.