don't pass rope_scaling kwarg if it's None (#383)

src/axolotl/utils/models.py

@@ -229,8 +229,12 @@ def load_model(
         elif cfg.is_llama_derived_model and not cfg.trust_remote_code:
             from transformers import LlamaForCausalLM
 
+            config_kwargs = {}
+            if cfg.rope_scaling:
+                config_kwargs["rope_scaling"] = cfg.rope_scaling
             config = LlamaConfig.from_pretrained(
-                base_model_config, rope_scaling=cfg.rope_scaling
+                base_model_config,
+                **config_kwargs,
             )
             model = LlamaForCausalLM.from_pretrained(
                 base_model,