fix: AWS Lambda collector.

src/instana/agent/serverless.py

@@ -153,7 +153,7 @@ def _prepare_payload(self, payload: dict[str, Any]) -> dict[str, Any]:
         Returns:
             Modified payload with filtered spans
         """
-        spans = payload.get("spans", [])
+        spans = payload.get("spans") or []
         filtered_spans = self.filter_spans(spans)
 
         if len(filtered_spans) > 0:

src/instana/collector/aws_lambda.py

@@ -46,8 +46,8 @@ def should_send_snapshot_data(self):
 
     def prepare_payload(self):
         payload = DictionaryOfStan()
-        payload["spans"] = None
-        payload["metrics"] = None
+        payload["spans"] = []
+        payload["metrics"]["plugins"] = []
 
         if not self.span_queue.empty():
             payload["spans"] = format_span(self.queued_spans())

tests/agent/test_serverless_agent.py

@@ -205,6 +205,18 @@ def test_prepare_payload_with_no_spans(self) -> None:
         assert "metrics" in result
         assert "spans" not in result or len(result.get("spans", [])) == 0
 
+    def test_prepare_payload_with_none_spans(self) -> None:
+        """Test payload preparation when spans are explicitly None."""
+        agent = ConcreteServerlessAgent()
+
+        payload = {"spans": None, "metrics": {"test": "data"}}
+
+        result = agent._prepare_payload(payload)
+
+        assert "metrics" in result
+        # Should handle None spans without raising a TypeError
+        assert result["spans"] is None
+
     def test_build_headers(self) -> None:
         """Test that headers are built correctly."""
         agent = ConcreteServerlessAgent()

tests/collector/test_aws_lambda_collector.py

@@ -0,0 +1,70 @@
+# (c) Copyright IBM Corp. 2026
+
+"""
+Unit tests for AWSLambdaCollector.
+This test suite validates the payload preparation and metric reporting
+for the AWS Lambda instrumentation collector.
+"""
+
+from collections import defaultdict
+from typing import Generator
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from instana.collector.aws_lambda import AWSLambdaCollector
+
+
+class TestAWSLambdaCollector:
+    """Test suite for AWSLambdaCollector base class."""
+
+    @pytest.fixture(autouse=True)
+    def _resource(
+        self,
+        caplog: pytest.LogCaptureFixture,
+    ) -> Generator[None, None, None]:
+
+        self.agent = MagicMock()
+        self.collector = AWSLambdaCollector(self.agent)
+        yield
+
+    def test_prepare_payload_empty_span_queue(self) -> None:
+        """Test that prepare_payload returns an empty list for spans when queue is empty."""
+        payload = self.collector.prepare_payload()
+
+        assert isinstance(payload, defaultdict)
+
+        assert "spans" in payload
+        assert payload["spans"] == []
+
+        assert "metrics" in payload
+        assert "plugins" in payload["metrics"]
+
+    def test_prepare_payload_with_spans(self) -> None:
+        """Test that prepare_payload formats queued spans and includes them in the payload."""
+        mock_span = MagicMock()
+        self.collector.span_queue.put(mock_span)
+
+        # Mock queued_spans and format_span
+        self.collector.queued_spans = MagicMock(return_value=[mock_span])
+
+        with patch("instana.collector.aws_lambda.format_span") as mock_format:
+            mock_format.return_value = [{"n": "test_span"}]
+            payload = self.collector.prepare_payload()
+
+        assert payload["spans"] == [{"n": "test_span"}]
+        assert payload["metrics"]["plugins"] == []
+
+    def test_prepare_payload_with_snapshot_data(self) -> None:
+        """Test that prepare_payload includes snapshot data when it should be sent."""
+        self.collector.snapshot_data = {
+            "plugins": [{"name": "com.instana.plugin.aws.lambda"}]
+        }
+        self.collector.snapshot_data_sent = False
+
+        payload = self.collector.prepare_payload()
+
+        assert payload["metrics"] == {
+            "plugins": [{"name": "com.instana.plugin.aws.lambda"}]
+        }
+        assert self.collector.snapshot_data_sent is True