Antenna Array Factor Null Steering

You can choose one direction and compute the steering vectors for each element. In essence, you can compute the steering vectors youself and just do the last part of the code

% steering vector for null direction
wn
% steering vectors for lookout direction
wd
% Compute the response of desired steering at null direction
rn = wn'*wd/(wn'*wn);
% Sidelobe canceler - remove the response at null direction
w = wd-wn*rn;

Full code:

c = 3e8;        % signal propagation speed
fc = 1e9;       % signal carrier frequency
lambda = c/fc;  % wavelength
thetaad = -30:5:30;     % look directions
thetaan = 40;           % interference direction
ula = phased.ULA(10,lambda/2);
ula.Element.BackBaffled = true;
% Calculate the steering vector for null directions
wn = steervec(getElementPosition(ula)/lambda,thetaan);
% Calculate the steering vectors for lookout directions
wd = steervec(getElementPosition(ula)/lambda,thetaad);
% Compute the response of desired steering at null direction
rn = wn'*wd/(wn'*wn);
% Sidelobe canceler - remove the response at null direction
w = wd-wn*rn;
% Plot the pattern
pattern(ula,fc,-180:180,0,'PropagationSpeed',c,'Type','powerdb',...
    'CoordinateSystem','rectangular','Weights',w);
hold on; legend off;
plot([40 40],[-100 0],'r--','LineWidth',2)
text(40.5,-5,'\leftarrow Interference Direction','Interpreter','tex',...
    'Color','r','FontSize',10)