ValueError: Nonlinear objective functions are not supported!

[FCYtheFreeman]

My integer programming has multiple solutions，and I want to find the best solution that has the minimum number of 0.
Since my variables is non-negative integer, and the sum of variables is confirmed，my first method is set model.setObjective(x^2 + y^2 + z^2 , "maximize"), but it leads to an error:
ValueError: Nonlinear objective functions are not supported!

How can I solve this problem？Or is there other ways I can achieve my goal？

Thank you !

[fserra]

check my answer in #167