fix(semantic-layer): omit null dimension values instead of converting to empty string

Null values are not valid filter values and would produce invalid where
clauses if returned. Also adds a test covering null omission and corrects
the changelog entry describing the list[str] fix.

Author: b-per

.changes/unreleased/Bug Fix-20260519-142146.yaml

@@ -1,3 +1,3 @@
 kind: Bug Fix
-body: 'Fix get_dimension_values: widen values type to list[Any], add error handling, add limit >= 1 validation'
+body: 'Fix get_dimension_values: stringify dimension values to maintain list[str] type, omit nulls, add error handling, add limit >= 1 validation'
 time: 2026-05-19T14:21:46.951552+02:00

src/dbt_mcp/semantic_layer/client.py

@@ -372,9 +372,9 @@ async def get_dimension_values(
                     metrics=metrics or [],
                     group_by=dimension,
                 )
+            # SDK doesn't support server-side limiting; truncation is applied client-side.
             raw: list[str] = [
-                str(v) if v is not None else ""
-                for v in raw_table.column(dimension).to_pylist()
+                str(v) for v in raw_table.column(dimension).to_pylist() if v is not None
             ]
             truncated = len(raw) > limit
             return DimensionValuesResponse(values=raw[:limit], truncated=truncated)

tests/unit/semantic_layer/test_client.py

@@ -1027,3 +1027,35 @@ async def test_get_dimension_values_no_metrics_passes_empty_list(mock_client_pro
     )
     assert result.values == ["active", "inactive"]
     assert result.truncated is False
+
+
+@pytest.mark.asyncio
+async def test_get_dimension_values_omits_nulls(mock_client_provider):
+    mock_sl_client = MagicMock()
+    session_ctx = MagicMock()
+    mock_sl_client.session.return_value = session_ctx
+    session_ctx.__enter__ = MagicMock(return_value=mock_sl_client)
+    session_ctx.__exit__ = MagicMock(return_value=False)
+    mock_sl_client.dimension_values.return_value = pa.table(
+        {"customer__country": pa.array(["US", None, "FR"], type=pa.string())}
+    )
+    mock_client_provider.get_client.return_value = mock_sl_client
+
+    token_p = MagicMock()
+    token_p.get_token.return_value = "tok"
+    headers_p = MagicMock()
+    headers_p.get_headers.return_value = {}
+    config = SemanticLayerConfig(
+        url="https://test-host/api/graphql",
+        host="test-host",
+        prod_environment_id=123,
+        token_provider=token_p,
+        headers_provider=headers_p,
+    )
+    fetcher = SemanticLayerFetcher(client_provider=mock_client_provider)
+    result = await fetcher.get_dimension_values(
+        config=config, dimension="customer__country", metrics=None, limit=100
+    )
+
+    assert result.values == ["US", "FR"]
+    assert result.truncated is False