Reset type for `$callback` var since it's not really a callback
Reset type for `$callback` var since it's not really a callback

RequestTest treats it as a string, so we'll treat it as a string here,
too.

lornajane/joindin-api,heiglandreas/joindin-api,joindin/joindin-api,heiglandreas/joindin-api,dstockto/joindin-api,railto/joindin-api,joindin/joindin-api,heiglandreas/joindin-api,dstockto/joindin-api,dstockto/joindin-api,railto/joindin-api,joindin/joindin-api,railto/joindin-api,lornajane/joindin-api,lornajane/joindin-api