BI Publisher condition : display if is not null

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Hello, 

I create my job offer letter via BI Publisher plug in on Word.

I create a conditional region in order to display a sentence  If ATTRIBUTE_NUMBER5 is not null. 

I found this formula in order to do this <?if:ATTRIBUTE_NUMBER5="?> ... <?end if?>.

However it seems does not work. When I load in the tool for the recruiting module, the offer letter cannot be load (white page). When I remove my formula, my job offer letter can be load. 

Could you confirm my formula and maybe explain me where is my issue. 

Thank you,