The feedback voltage could be as far off as +/-0.012 volts so the feedback parallel resistance should not be any higher than the worst case voltage error of 0.012 volts divided by the worst case input bias current of 50 nanoamps or 240 kilohms to double the error.
In practice, it will be much lower than this and typically the AC impedance at the feedback pin needs to be low anyway to prevent capacitive coupling into it from preventing proper operation.