fix: handle empty gremlin examples when building index

[Gardenia-zx]

Purpose

This PR handles the empty examples case in BuildGremlinExampleIndex.

Previously, when examples was empty, run() could access examples_embedding[0] and raise an IndexError.

Changes

• Return early when examples is empty.
• Return early when generated embeddings are empty.
• Update the unit test to verify that no embedding or vector index operation is triggered for empty examples.
• Adjust the mock target to avoid coroutine warnings in tests.

Tests

uv run pytest src/tests/operators/index_op/test_build_gremlin_example_index.py -v

[Copilot]

Pull request overview

This PR fixes an IndexError in BuildGremlinExampleIndex.run() by safely handling the case where no Gremlin examples (or no embeddings) are produced, and updates unit tests to assert that embedding/vector-index operations are skipped in those cases.

Changes:

• Add an early return in BuildGremlinExampleIndex.run() when examples is empty (sets context["embed_dim"]=0).
• Add an early return when the generated embeddings list is empty (avoids examples_embedding[0] access).
• Update unit tests to validate “no-op” behavior for empty examples and adjust mocking to prevent coroutine warnings.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
hugegraph-llm/src/hugegraph_llm/operators/index_op/build_gremlin_example_index.py	Adds guards for empty examples / empty embeddings to avoid indexing into an empty list and to skip vector index operations.
hugegraph-llm/src/tests/operators/index_op/test_build_gremlin_example_index.py	Updates mocks and assertions to ensure no embedding/index calls happen when examples are empty, and verifies embed_dim is set to 0.

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[imbajin]

‼️ BuildGremlinExampleIndexNode.node_init() still rejects [] via if not self.wk_input.examples (hugegraph-llm/src/hugegraph_llm/nodes/index_node/build_gremlin_example_index.py:37), so the main BuildExampleIndexFlow never reaches this branch for the empty-list case. As written, the unit test passes but the end-to-end workflow still returns examples is required. Could we align the node-level guard in the same PR or add flow-level coverage?

[imbajin]

‼️ Returning early here leaves any previously persisted gremlin_examples index untouched. GremlinExampleIndexQuery reuses that index whenever exist("gremlin_examples") is true, so rebuilding with an empty example set will still serve stale examples from the previous run. If an empty list is meant to clear the few-shot examples, we should wipe the index before returning.

Suggested change

	return context
	if not self.examples:
	self.vector_index.clean(self.vector_index_name)
	context["embed_dim"] = 0
	return context