docs: def _maximize(self):
          """ Find argmax of the acquisition function."""
          if not self.space.is_observations_valid():
              return None
          y_max = self.space.y.max()
          self.utility_function.gaussian_process.fit(self.space.x, self.space.y)
          return self.utility_function.max_compute(y_max=y_max,
                                                   bounds=self.space.bounds,
                                                   n_warmup=self.n_warmup,
                                                   n_iter=self.n_iter)