Insert "Nan" in Interpolated data from GRIDDATA that fall outside known data

Below is my code. I'm using interpoltation on the grid points using 'griddata'.

Currently the range of mesh grid which I have given is out of my sample dataset . As it is doing interpolation then why it is calculating "Vq" in query region which is outside our sample dataset. It should give NaN in that region.

~ Also if it does so then can how can we insert 'NaN' in the zone which is outside of our sample dataset ?

Thanks in Advance

clear all; clc;
F = importdata('Data.txt'); % X; Y; V;
F = F.data;
X = F(:,1); Y = F(:,2); V = F(:,3); % known values
[Xg,Yg] = meshgrid(-51:0.2:-49,10:0.1:20);
Vq = griddata(X,Y,V,Xg,Yg);