added default value for log_reward_clip_min in abstract base class

src/gfn/gflownet/base.py

@@ -24,6 +24,7 @@ class GFlowNet(ABC, nn.Module, Generic[TrainingSampleType]):
 
     A formal definition of GFlowNets is given in Sec. 3 of [GFlowNet Foundations](https://arxiv.org/pdf/2111.09266).
     """
+    log_reward_clip_min = float("-inf")  # Default off.
 
     @abstractmethod
     def sample_trajectories(
@@ -214,7 +215,7 @@ def get_trajectories_scores(
         total_log_pb_trajectories = log_pb_trajectories.sum(dim=0)
 
         log_rewards = trajectories.log_rewards
-        # TODO: log_reward_clip_min isn't defined in base (#155).
+
         if math.isfinite(self.log_reward_clip_min) and log_rewards is not None:
             log_rewards = log_rewards.clamp_min(self.log_reward_clip_min)