Project Import can throw a NPE when importing data with invalid custom field configuration.

java.util.concurrent.ExecutionException: java.lang.NullPointerException
 at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
 at java.util.concurrent.FutureTask.get(FutureTask.java:83)
 at com.atlassian.jira.task.TaskDescriptorImpl.getResult(TaskDescriptorImpl.java:114)
 at com.atlassian.jira.web.bean.TaskDescriptorBean.getResult(TaskDescriptorBean.java:77)
 at com.atlassian.jira.web.action.admin.importer.project.ProjectImportBackupOverviewProgress.handleFinishedTask(ProjectImportBackupOverviewProgress.java:34)
 at com.atlassian.jira.web.action.admin.importer.project.AbstractProjectImportProgress.doExecute(AbstractProjectImportProgress.java:63)
 at webwork.action.ActionSupport.execute(ActionSupport.java:153)
 at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:59)
 at webwork.dispatcher.GenericDispatcher.executeAction(GenericDispatcher.java:141)
 at com.atlassian.jira.web.dispatcher.JiraServletDispatcher.service(JiraServletDispatcher.java:181)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
 ...
Caused by: java.lang.NullPointerException
 at com.atlassian.jira.imports.project.core.BackupOverviewBuilderImpl.getIssueTypesList(BackupOverviewBuilderImpl.java:282)
 at com.atlassian.jira.imports.project.core.BackupOverviewBuilderImpl.getCustomFieldConfigurations(BackupOverviewBuilderImpl.java:220)
 at com.atlassian.jira.imports.project.core.BackupOverviewBuilderImpl.getProjects(BackupOverviewBuilderImpl.java:187)
 at com.atlassian.jira.imports.project.core.BackupOverviewBuilderImpl.getBackupOverview(BackupOverviewBuilderImpl.java:115)
 at com.atlassian.jira.imports.project.handler.BackupOverviewHandler.getBackupOverview(BackupOverviewHandler.java:28)
 at com.atlassian.jira.imports.project.DefaultProjectImportManager.getBackupOverview(DefaultProjectImportManager.java:184)
 at com.atlassian.jira.bc.imports.project.DefaultProjectImportService.getBackupOverview(DefaultProjectImportService.java:180)
 at com.atlassian.jira.web.action.admin.importer.project.ProjectImportSelectBackup$BackupOverviewCallable.call(ProjectImportSelectBackup.java:199)
 at com.atlassian.jira.web.action.admin.importer.project.ProjectImportSelectBackup$BackupOverviewCallable.call(ProjectImportSelectBackup.java:187)
 at com.atlassian.jira.task.TaskManagerImpl$TaskCallableDecorator.call(TaskManagerImpl.java:338)
 at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
 at java.util.concurrent.FutureTask.run(FutureTask.java:138)
 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)