[Developers] how to get items with properties having null values?

[Raymond Yee]

Hi everyone,

I'd like to pull up all chemical elements whose boiling points are null 
(i.e., that have no value).  Using parallax, you can see a table of 
elements along with the boiling points:

http://mqlx.com/~david/parallax/browse.html?state=!((d:(t:/chemistry/chemical_element),s:(v:!((c:ThumbnailView,s:()),(c:TabularView,s:(asc:!t,c:(s:!f),cols:!((p:(d:!(),s:!t)),(p:(d:!(!((f:!t,p:/chemistry/chemical_element/boiling_point))),s:!t))),sort:0))),vi:1)))

or

http://is.gd/iY45

(hit "Render Table")

I figured out how to get elements whose boiling points are not null by 
asking for "boiling_point<" : 100000 -- since all real elements have bp 
< 1000000 C but any null elements would return false:

http://is.gd/iY6k

query is:

[
  {
    "atomic_number" : null,
    "boiling_point" : null,
    "boiling_point<" : 100000,
    "name" : null,
    "sort" : "atomic_number",
    "type" : "/chemistry/chemical_element"
  }
]

The question I have is how to ask for non-null values more directly.  
How do I say something like

"boiling_point!=" : null

-Raymond