Australian passport holders applying for a China visa Whilst in New Zealand

It seems from my reading, One of the requirements for applying for a China visa in NZ if New Zealand is a third country for the passport holder is that you provide proof you are allowed to be in New Zealand. I am not sure how to do this as Australian passport holders are allowed to freely come and go from New Zealand by law with no visa or other requirements. I will have no proof documents to put in my visa application and can only rely on the fact that its law Australians can stay indefinitely in NZ (and visa versa). Do you have any suggestions how I should deal with this issue when applying for a China visa from Nw Zealand, the issue must have come up many times before? Thanks