Genetic Algorithms problem with StepSize in mutationadaptfeasible function

Hi all, I'm working with GAs in optimtool. When I use it, during second iteration I received problem in mutationadaptfeasible function. In fact in every step it initialites StepSize = [] and after the second iteration it remains equal to []. So it crashes because I have 2 bounds. I modify the script in this way:

persistent StepSize
..

if state.Generation <=2

      StepSize = 1; % Initialization
  else
      if isfield(state,'Spread')
          if state.Spread(end) > state.Spread(end-1)
              StepSize = min(1,StepSize*4);
          else
              StepSize = max(sqrt(eps),StepSize/4);
          end
      else
          if state.Best(end) < state.Best(end-1)
              StepSize = min(1,StepSize*4);
          else
              StepSize = max(sqrt(eps),StepSize/4);
          end
      end
  end
if(sum(size(StepSize))==0)  <--- THIS
    StepSize = 1;
end
...
case 'boundconstraints'
         [Basis,TangentCone] = boxdirections(true,StepSize,x,linCon.lb,linCon.ub,tol); % NOW OK

Could be ok? Thanks to all