Details
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Bug
 - 
    Resolution: Fixed
 - 
    
Major
 - 
    1.0.1
 - 
    Windows 10 Pro 64 bit, Chrome v.63, Firefox v.57, IE v.11, Edge v.16 using a local instance XWiki 9.11 on PostgreSQL 10
 
- 
        Unknown
 - 
        
 
Description
STEPS TO REPRODUCE:
- Login with Admin or with an user
 - Set 'Display hidden pages' to 'YES' from Profile > Preferences > Display Preferences
 - Click on 'Templates' page from Navigation panel or from Page Index (/xwiki/bin/view/Templates/)
 - Observe the console
 
EXPECTED RESULTS
The 'Templates' page is displayed without any errors.
ACTUAL RESULTS
The 'Template' page opens, followed by an error in console, having the following stacktrace:
2017-12-22 13:31:04,028 [http://localhost:8080/xwiki/bin/get/Templates/WebHome?outputSyntax=plain&sheet=XWiki.DocumentTree&root=space%3ATemplates&root=space%3ATemplates&data=children&id=%23] ERROR o.x.v.i.DefaultVelocityEngine  - Left side ($childNodeIds.size()) of '>=' operation has null value at 43:xwiki:XWiki.DocumentTree[line 144, column 29]
The issue reproduces also on previous XWiki versions (tested down to 8.4.5).