White Spot in Shadow

I created my model in voxel editor and imported into Unity. However the shadow looked weird, there was some white spot in the shadow. I tried different option to export the model and got the same result. Both of MagicaVoxel and Qubicle had the same issue. Please help me.

I don’t know MagicaVoxel or Qubicle but to me, there is simply a small gap between your faces.