[Bugfix] fix cache session id in chat method (#1107)

Co-authored-by: Deven Patel <deven298@yahoo.com>

embedchain/llm/gpt4all.py

@@ -1,3 +1,5 @@
+import os
+from pathlib import Path
 from typing import Iterable, Optional, Union
 
 from langchain.callbacks.stdout import StdOutCallbackHandler
@@ -29,7 +31,14 @@ class GPT4ALLLlm(BaseLlm):
                 "The GPT4All python package is not installed. Please install it with `pip install --upgrade embedchain[opensource]`"  # noqa E501
             ) from None
 
-        return LangchainGPT4All(model=model)
+        model_path = Path(model).expanduser()
+        if os.path.isabs(model_path):
+            if os.path.exists(model_path):
+                return LangchainGPT4All(model=str(model_path))
+            else:
+                raise ValueError(f"Model does not exist at {model_path=}")
+        else:
+            return LangchainGPT4All(model=model, allow_download=True)
 
     def _get_answer(self, prompt: str, config: BaseLlmConfig) -> Union[str, Iterable]:
         if config.model and config.model != self.config.model: