PID controller tuning with GA optimization errer

i used simulink for PID controller with GA

code

function z = pidgam(x)

kp=x(1);

ki=x(2);

kd=x(3);

out = sim('pidga.slx','SrcWorkspace','Current');

iae = sum(abs(out.get('error')));

y = iae;

z = y;

and gatool

para = 3

use optimtool get error

Optimization running. Error running optimization. Undefined function 'abs' for input arguments of type 'timeseries'.

um... help me