# Error when building slab as roof

**URL:** <https://discourse.stonehearth.net/t/error-when-building-slab-as-roof/17824>\
**Category:** Other Reports\
**Tags:** duplicate\
**Created:** [November 17, 2015, 7:12am UTC](https://discourse.stonehearth.net/t/error-when-building-slab-as-roof/17824 "2015-11-17T07:12:09Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![BacMan12](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.stonehearth.net/bacman12/32/15643_2.png) [@BacMan12](https://discourse.stonehearth.net/u/BacMan12)\
**Post date:** [November 17, 2015, 7:12am UTC](https://discourse.stonehearth.net/t/error-when-building-slab-as-roof/17824/1 "2015-11-17T07:12:09Z")

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Got this error while i was trying to build a slag as roof upon some pillars

## Like this

 ![](https://us1.discourse-cdn.com/flex022/uploads/stonehearth/original/3X/5/3/5370788ef8a2f1d507c2edbd7b47bc07f7d0c1f7.jpg)

## Then this happened

 ![](https://us1.discourse-cdn.com/flex022/uploads/stonehearth/original/3X/f/d/fda824b94d860b4af73edfd13b99b09a7d5cc098.jpg)

## Here is the error

develop-2697 (x64)  
…nehearth/components/building/building\_component.luac:124: attempt to index local ‘entity’ (a nil value)  
stack traceback:  
radiant/modules/events.luac:84: in function \<radiant/modules/events.luac:81\>  
…nehearth/components/building/building\_component.luac:124: in function ‘\_trace\_entity’  
…nehearth/components/building/building\_component.luac:37: in function ‘\_restore\_structure\_traces’  
…nehearth/components/building/building\_component.luac:17: in function ‘obj’  
radiant/modules/events.luac:44: in function ‘instance’  
radiant/modules/events.luac:98: in function \<radiant/modules/events.luac:96\>  
[C]: in function ‘xpcall’  
radiant/modules/events.luac:96: in function \<radiant/modules/events.luac:86\>

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<div class="post-metadata">

**Author:** ![jomaxro](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.stonehearth.net/jomaxro/32/47935_2.png) [@jomaxro](https://discourse.stonehearth.net/u/jomaxro)\
**Post date:** [November 17, 2015, 7:22am UTC](https://discourse.stonehearth.net/t/error-when-building-slab-as-roof/17824/2 "2015-11-17T07:22:38Z")

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6 posts were merged into an existing topic: [Building error (undo or console delete related)](https://discourse.stonehearth.net/t/building-error-undo-or-console-delete-related/16633)