community: Fix ValidationError on creating GPT4AllEmbeddings with no gpt4all_kwargs (#25124)

- **Description:** Instantiating `GPT4AllEmbeddings` with no
`gpt4all_kwargs` argument raised a `ValidationError`. Root cause: #21238
added the capability to pass `gpt4all_kwargs` through to the `GPT4All`
instance via `Embed4All`, but broke code that did not specify a
`gpt4all_kwargs` argument.
- **Issue:** #25119 
- **Dependencies:** None
- **Twitter handle:** [`@metadaddy`](https://twitter.com/metadaddy)

libs/community/langchain_community/embeddings/gpt4all.py

@@ -38,7 +38,7 @@ class GPT4AllEmbeddings(BaseModel, Embeddings):
                 model_name=values.get("model_name"),
                 n_threads=values.get("n_threads"),
                 device=values.get("device"),
-                **values.get("gpt4all_kwargs"),
+                **(values.get("gpt4all_kwargs") or {}),
             )
         except ImportError:
             raise ImportError(

libs/community/tests/unit_tests/embeddings/test_gpt4all.py

@@ -0,0 +1,62 @@
+import sys
+from typing import Any, Optional
+from unittest.mock import MagicMock, patch
+
+from langchain_community.embeddings import GPT4AllEmbeddings
+
+_GPT4ALL_MODEL_NAME = "all-MiniLM-L6-v2.gguf2.f16.gguf"
+_GPT4ALL_NTHREADS = 4
+_GPT4ALL_DEVICE = "gpu"
+_GPT4ALL_KWARGS = {"allow_download": False}
+
+
+class MockEmbed4All(MagicMock):
+    """Mock Embed4All class."""
+
+    def __init__(
+        self,
+        model_name: Optional[str] = None,
+        *,
+        n_threads: Optional[int] = None,
+        device: Optional[str] = None,
+        **kwargs: Any,
+    ):  # type: ignore[no-untyped-def]
+        assert model_name == _GPT4ALL_MODEL_NAME
+
+
+class MockGpt4AllPackage(MagicMock):
+    """Mock gpt4all package."""
+
+    Embed4All = MockEmbed4All
+
+
+def test_create_gpt4all_embeddings_no_kwargs() -> None:
+    """Test fix for #25119"""
+    with patch.dict(sys.modules, {"gpt4all": MockGpt4AllPackage()}):
+        embedding = GPT4AllEmbeddings(  # type: ignore[call-arg]
+            model_name=_GPT4ALL_MODEL_NAME,
+            n_threads=_GPT4ALL_NTHREADS,
+            device=_GPT4ALL_DEVICE,
+        )
+
+        assert embedding.model_name == _GPT4ALL_MODEL_NAME
+        assert embedding.n_threads == _GPT4ALL_NTHREADS
+        assert embedding.device == _GPT4ALL_DEVICE
+        assert embedding.gpt4all_kwargs == {}
+        assert isinstance(embedding.client, MockEmbed4All)
+
+
+def test_create_gpt4all_embeddings_with_kwargs() -> None:
+    with patch.dict(sys.modules, {"gpt4all": MockGpt4AllPackage()}):
+        embedding = GPT4AllEmbeddings(  # type: ignore[call-arg]
+            model_name=_GPT4ALL_MODEL_NAME,
+            n_threads=_GPT4ALL_NTHREADS,
+            device=_GPT4ALL_DEVICE,
+            gpt4all_kwargs=_GPT4ALL_KWARGS,
+        )
+
+        assert embedding.model_name == _GPT4ALL_MODEL_NAME
+        assert embedding.n_threads == _GPT4ALL_NTHREADS
+        assert embedding.device == _GPT4ALL_DEVICE
+        assert embedding.gpt4all_kwargs == _GPT4ALL_KWARGS
+        assert isinstance(embedding.client, MockEmbed4All)