How to define if object is equal to null in magnolia freemarker(.ftl)

I am currently working on piece of component, I need an if else statement to be done to filter out wether a page object is null or not, here is my attempts:

[#assign page = cmsfn.page(component)]
[#if page IS NULL ] // not working...
   [@cms.component content=cmsfn.asContentMap(component) editable=false/]
[/#if]

and this one

[#assign page = cmsfn.page(component)]
[#if !page?has_content ] // not working...
   [@cms.component content=cmsfn.asContentMap(component) editable=false/]
[/#if]

What I am trying to do here is, if the page object is null , then do the component rending, these page object are jrc children nodes, when rendering component this type of node mess up thing template, so I need to filter out and make sure the page is null, then render.

Any suggestions? please provide me a code example. Thanks

Solution

The template language of FreeMarker (2.x) has this... quirk, that it doesn't have a null value. Thus, you can't store null in a variable. When you have foo.bar where bar corresponds to Java getBar() which return null, then as far as the template language is concerned, foo simply doesn't contain bar. And, referring to something that doesn't exist is illegal, unless, you apply a null/missing handler operator directly on the referring expression (like foo.bar!'myDefault' or foo.bar??).

So the simplest approach is to avoid the assignment like [#if cmsfn.page(component)??]...[/#if]. But sometimes that's not acceptable as then you have to get the page for a second time further down. Then you can use some default that you can differentiate from the non-default. Assuming that for a page object ?has_content gives true (and unless you are using some strange ObjectWrapper it does), a default value like {} (empty hash) suffices. The exp! operator can be used as a shorthand, as it also gives a default value for which ?has_content is false:

[#assign page = cmsfn.page(component)!]
[#if page?has_content]
   [@cms.component content=cmsfn.asContentMap(component) editable=false/]
   ... Do something with `page`, otherwise we need not use #assign.
[#else]
   ... Don't do anything with `page`, it's that strange default object.
[/#if]