Put m-file to simulink, why it don't work?

I have m-file where is next code:

if true
   function y=fun(eka,toka,kolmas,neljas,viides,ti) 
%#codegen
coder.extrinsic('spline');
coder.extrinsic('apu');
x=[eka toka kolmas neljas viides];
xx=[ti:ti+4];
apu = spline(xx,x,xx);
y=apu;

end

Why this don't work? It gives error message: function output 'y' cannot be an mxArray in this context. Consider preinitializing the output variable with a known type.

What I do wrong?