[Bugfix] Fix corner case of sparse embedding (#33886)

Signed-off-by: wang.yuqi <yuqi.wang@daocloud.io>

tests/models/language/pooling/test_bge_m3.py

@@ -136,6 +136,16 @@ async def test_bge_m3_api_server_sparse_embedding(client: openai.AsyncOpenAI):
     )
 
 
+@pytest.mark.asyncio
+async def test_bge_m3_api_server_sparse_embedding_corner_case(
+    client: openai.AsyncOpenAI,
+):
+    embeddings = await sparse_embeddings(client, ["Hi"])
+    assert len(embeddings) == 1
+    assert 2673 in embeddings[0]
+    assert embeddings[0][2673] == pytest.approx(0.26710861921310425, rel=0.01)
+
+
 # https://github.com/FlagOpen/FlagEmbedding/blob/6fd176266f2382878bcc69cd656cff425d52f49b/FlagEmbedding/inference/embedder/encoder_only/m3.py#L163
 def colbert_score(q_reps: torch.Tensor, p_reps: torch.Tensor) -> torch.Tensor:
     token_scores = torch.einsum("in,jn->ij", q_reps, p_reps)