Add import error checks for mergekit extra

trl/mergekit_utils.py

@@ -71,6 +71,10 @@ class MergeConfig:
     """
 
     def __init__(self, method: str = "linear"):
+        if not is_mergekit_available():
+            raise ImportError(
+                "MergeConfig requires the `mergekit` extra. To install, run `pip install trl[mergekit]`."
+            )
         self.method = method
         self.policy_model_path = None
         self.target_model_path = None
@@ -265,6 +269,8 @@ def merge_models(config: MergeConfig, out_path: str):
         config (`MergeConfig`): The merge configuration.
         out_path (`str`): The output path for the merged model.
     """
+    if not is_mergekit_available():
+        raise ImportError("merge_models requires the `mergekit` extra. To install, run `pip install trl[mergekit]`.")
     run_merge(
         config,
         out_path=out_path,