fixing from_documents method of the MongoDB Atlas vector store (#5794)

FIxed a bug in from_documents method --> Collection objects do not
implement truth value testing or bool().
@dev2049

langchain/vectorstores/mongodb_atlas.py

@@ -262,7 +262,7 @@ class MongoDBAtlasVectorSearch(VectorStore):
                     collection=collection
                 )
         """
-        if not collection:
+        if collection is None:
             raise ValueError("Must provide 'collection' named parameter.")
         vecstore = cls(collection, embedding, **kwargs)
         vecstore.add_texts(texts, metadatas=metadatas)