Update api/models/dataset.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

api/models/dataset.py

@@ -60,7 +60,7 @@ class Dataset(Base):
     updated_by = mapped_column(StringUUID, nullable=True)
     updated_at = mapped_column(db.DateTime, nullable=False, server_default=func.current_timestamp())
     embedding_model: Mapped[str] = mapped_column(db.String(255), nullable=True)
-    embedding_model_provider: Mapped[str] = mapped_column(db.String(255), nullable=True)
+    embedding_model_provider: Mapped[Optional[str]] = mapped_column(db.String(255), nullable=True)
     collection_binding_id = mapped_column(StringUUID, nullable=True)
     retrieval_model = mapped_column(JSONB, nullable=True)
     built_in_field_enabled = mapped_column(db.Boolean, nullable=False, server_default=db.text("false"))