Bugzilla importer breaks with NullPointerException if Improvement or Bug issue type doesn't exist

Error importing data from bugzilla: 
java.lang.NullPointerException
 at com.atlassian.jira.workflow.SimpleWorkflowManager.createIssue(SimpleWorkflowManager.java:130)
 at com.atlassian.jira.issue.managers.DefaultIssueManager.createIssue(DefaultIssueManager.java:299)
 at com.atlassian.jira.issue.managers.DefaultIssueManager.createIssue(DefaultIssueManager.java:247)
 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:585)
 at com.atlassian.util.profiling.object.ObjectProfiler.profiledInvoke(ObjectProfiler.java:71)
 at com.atlassian.jira.config.component.SwitchingInvocationHandler.invoke(SwitchingInvocationHandler.java:28)
 at $Proxy3.createIssue(Unknown Source)
 at com.atlassian.jira.util.BugzillaImportBean.createIssue(BugzillaImportBean.java:387)
 at com.atlassian.jira.util.BugzillaImportBean.createIssues(BugzillaImportBean.java:307)
 at com.atlassian.jira.util.BugzillaImportBean.create(BugzillaImportBean.java:200)
 at com.atlassian.jira.web.action.util.BugzillaImport.doRun(BugzillaImport.java:150)
 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:585)
...