As reported by Clifford in the mailing list:
this outputs null because the array field is not initialized.
The PDF specification has this:
A colour space shall be defined by an array object whose first element is a name object identifying the colour space family. The remaining array elements, if any, are parameters that further characterize the colour space; their number and types vary according to the particular family. For families that do not require parameters, the colour space may be specified simply by the family name itself instead of an array.