Fix bug on empty openmetrics scrape response (#14508)

datadog_checks_base/datadog_checks/base/checks/openmetrics/v2/scraper.py

@@ -285,7 +285,11 @@ def parse_metrics(self):
         # Since we determine `self.parse_metric_families` dynamically from the response and that's done as a
         # side effect inside the `line_streamer` generator, we need to consume the first line in order to
         # trigger that side effect.
-        line_streamer = chain([next(line_streamer)], line_streamer)
+        try:
+            line_streamer = chain([next(line_streamer)], line_streamer)
+        except StopIteration:
+            # If line_streamer is an empty iterator, next(line_streamer) fails.
+            return
 
         for metric in self.parse_metric_families(line_streamer):
             self.submit_telemetry_number_of_total_metric_samples(metric)

openmetrics/tests/test_openmetrics.py

@@ -101,3 +101,12 @@ def test_openmetrics_use_latest_spec(aggregator, dd_run_check, mock_http_respons
     assert scraper.http.options['headers']['Accept'] == (
         'application/openmetrics-text;version=1.0.0,application/openmetrics-text;version=0.0.1'
     )
+
+
+def test_openmetrics_empty_response(aggregator, dd_run_check, mock_http_response, openmetrics_payload, caplog):
+    mock_http_response("")
+
+    check = OpenMetricsCheck('openmetrics', {}, [instance_new])
+    dd_run_check(check)
+
+    aggregator.assert_all_metrics_covered()