When trying to import a data without having the initial created users in the XML file. JIRA will show the following error message on the screen:

An error occurred whilst rendering this message. Please contact the administrators, and inform them of this bug. 
Details: ------- java.lang.NullPointerException at com.opensymphony.user.User.getFullName(User.java:83) 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:597) at 
org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java
....

The steps of replication are:

• Install a new instance of JIRA
• Setup the instance with a new Administration login.
• Login to JIRA with the new administrator.
• Go to Administrator->Import&Export->Restore data
• Then perform the import process.

Please note that the backup.xml file does not contain the username that is used to log in to the current JIRA instance. Once the data has successfully imported, the error message will prompt in the login page. Please refer to the screenshot for a clearer picture.