J-1 visa holder applying for German research visa

I am currently in the US as a J-1 visa holder, and I am applying for a researcher visa in Germany soon.

I have noticed that in the visa application form there is a field for "residence permit number" and the corresponding expiration date, but I am unsure as to what to write in that field, since the visa itself and the DS-2019 have different number and different expiration dates.

Could anyone inform me which of them is expected in the form?