I try to output my element only if the value of the property fileEn is NULL (fileEn => NULL)
<f:if condition="{file.fileEn}==NULL">
<f:debug title='file'>{file}</f:debug>
</f:if>
However this is also showing me elements where fileEn is not NULL!
You can't check if something is NULL like this, it works like this:
Render only if property is NULL:
<f:if condition="{file.fileEn}">
<f:then>
</f:then>
<f:else>
<!-- Property is NULL -->
<f:debug title='file'>{file}</f:debug>
</f:else>
</f:if>
Render only if property is NOT NULL:
<f:if condition="{file.fileEn}">
<!-- Property is not NULL -->
<f:debug title='file'>{file}</f:debug>
</f:if>