Really, saccharin as a well-known brightener, play a role of a stress reducer because its sulfonate groups recovers to sulphide. Then nichel sulphide deactivates catalytic centers in nichel and reduces the hydrogen saturation of deposits thereby promote stress reduction in thin nichel film.
Saccharin has amido and imido nitrogen. Owing to the presence of lone pairs on nitrogen atom, it participates to form π-interaction by donating lone pairs into d orbitals on the Nickel metal. Pie-interaction is a stabilizing factor which prevents to generating stress in the film.