Add null value in JSON

Hi,

I would like to have a service with a JSON as output.

Is it possible to add a 'null' value in an array there?

E.g.

{ 

field1: [50],

field2: [null],

field3: [60]

}

(My service returns 'Error executing service. Message ::null - See Script Error Log for more details').

The null is really necessary (NaN etc. are not an option).