Gas hob in alcove

[the2ems]

I have recently had an old fireplace opened up and the lintel raised in order to accommodate a range type cooker. The cooker will have electric ovens and gas hob. The inside of the newly formed alcove now needs to be tidied up, and the easiest way is to use plasterboard using the dot and dab method. But I have seen somewhere something about leaving voids. I'm not sure if this would apply to leaving voids behind the plasterboard where gas could possibly collect in the event of a leak. Could anyone confirm this for me please?

Thanks