fix: handle empty requests in milvus search to avoid connection attempts

[liferoad]

Prevent unnecessary connection attempts by returning early when receiving empty requests

apache_beam/ml/rag/enrichment/milvus_search_it_test.py:577: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/pipeline.py:670: in __exit__
    self.result = self.run()
                  ^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/testing/test_pipeline.py:118: in run
    result = super().run(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/pipeline.py:620: in run
    self._options).run(False)
                   ^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/pipeline.py:644: in run
    return self.runner.run_pipeline(self, self._options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/direct/direct_runner.py:245: in run_pipeline
    return runner.run_pipeline(pipeline, options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/fn_runner.py:196: in run_pipeline
    self._latest_run_result = self.run_via_runner_api(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/fn_runner.py:223: in run_via_runner_api
    return self.run_stages(stage_context, stages)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/fn_runner.py:470: in run_stages
    bundle_results = self._execute_bundle(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/fn_runner.py:795: in _execute_bundle
    self._run_bundle(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/fn_runner.py:1034: in _run_bundle
    result, splits = bundle_manager.process_bundle(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/fn_runner.py:1360: in process_bundle
    result_future = self._worker_handler.control_conn.push(process_bundle_req)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/portability/fn_api_runner/worker_handlers.py:389: in push
    response = self.worker.do_instruction(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/worker/sdk_worker.py:662: in do_instruction
    return getattr(self, request_type)(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/worker/sdk_worker.py:693: in process_bundle
    bundle_processor = self.bundle_processor_cache.get(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/worker/sdk_worker.py:514: in get
    processor = bundle_processor.BundleProcessor(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/runners/worker/bundle_processor.py:1135: in __init__
    op.setup(self.data_sampler)
apache_beam/runners/worker/operations.py:875: in apache_beam.runners.worker.operations.DoOperation.setup
    with self.scoped_start_state:
apache_beam/runners/worker/operations.py:925: in apache_beam.runners.worker.operations.DoOperation.setup
    self.dofn_runner.setup()
apache_beam/runners/common.py:1568: in apache_beam.runners.common.DoFnRunner.setup
    self._invoke_lifecycle_method(self.do_fn_invoker.invoke_setup)
apache_beam/runners/common.py:1564: in apache_beam.runners.common.DoFnRunner._invoke_lifecycle_method
    self._reraise_augmented(exn)
apache_beam/runners/common.py:1609: in apache_beam.runners.common.DoFnRunner._reraise_augmented
    raise new_exn
apache_beam/runners/common.py:1562: in apache_beam.runners.common.DoFnRunner._invoke_lifecycle_method
    lifecycle_method()
apache_beam/runners/common.py:602: in apache_beam.runners.common.DoFnInvoker.invoke_setup
    self.signature.setup_lifecycle_method.method_value()
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/apache_beam/io/requestresponse.py:340: in setup
    self._caller.__enter__()
apache_beam/ml/rag/enrichment/milvus_search.py:411: in __enter__
    self._client = MilvusClient(**connection_params)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/milvus_client/milvus_client.py:65: in __init__
    self._using = create_connection(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/milvus_client/_utils.py:49: in create_connection
    raise ex from ex
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/milvus_client/_utils.py:44: in create_connection
    connections.connect(
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/orm/connections.py:472: in connect
    connect_milvus(**kwargs, user=user, password=password, token=token, db_name=db_name)
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/orm/connections.py:426: in connect_milvus
    raise e from e
target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/orm/connections.py:418: in connect_milvus
    gh._wait_for_channel_ready(timeout=timeout)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <pymilvus.client.grpc_handler.GrpcHandler object at 0x7f48ab4447d0>
timeout = 10.0

    def _wait_for_channel_ready(self, timeout: Union[float] = 10):
        if self._channel is None:
            raise MilvusException(
                code=Status.CONNECT_FAILED,
                message="No channel in handler, please setup grpc channel first",
            )
    
        try:
            grpc.channel_ready_future(self._channel).result(timeout=timeout)
            self._setup_identifier_interceptor(self._user, timeout=timeout)
        except grpc.FutureTimeoutError as e:
            self.close()
>           raise MilvusException(
                code=Status.CONNECT_FAILED,
                message=f"Fail connecting to server on {self._address}, illegal connection params or server unavailable",
            ) from e
E           RuntimeError: pymilvus.exceptions.MilvusException: <MilvusException: (code=2, message=Fail connecting to server on localhost:46805, illegal connection params or server unavailable)> [while running 'Enrichment/Enrichment-RRIO/_Call/ParDo(_CallDoFn)']

target/.tox-py313-ml/py313-ml/lib/python3.13/site-packages/pymilvus/client/grpc_handler.py:162: RuntimeError

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[gemini-code-assist]

Summary of Changes

Hello @liferoad, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where the Milvus search component would attempt to connect to the Milvus server even when provided with an empty list of search requests, leading to unnecessary resource consumption and potential errors. The fix introduces a simple but effective early return for empty inputs, thereby optimizing the component's behavior and improving its robustness by avoiding futile connection attempts.

Highlights

• Prevented Unnecessary Connections: The change introduces an early exit mechanism to prevent the Milvus search component from attempting to establish a connection when there are no actual search requests to process.
• Optimized Empty Request Handling: An explicit check for empty input requests (reqs) has been added, ensuring that if the request list is empty, an empty result is returned immediately without further processing or connection attempts.

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