XF 2.2 Hide post username if member of group

[superfadi1]

I am trying to hide post username if he is a member of certain user group

The following conditional statement is working in template "post_macros" but with error "Template error: Cannot call method isMemberOf on a non-object (NULL)"

<xf:if is="$post.User.isMemberOf([x,y,z])">

<xf:macro template="message_macros" name="user_info" arg-user="{$post.User}"
arg-fallbackName="{$post.username}"/>

</xf:if>

I am running medical Q&A forum & need to hide the questioner name.

Thanks

 

[superfadi1]

I fixed it. Here is correct conditional statement

<xf:if is="$post.User AND {{$post.User.isMemberOf([x,y,z])}}">


</xf:if>