Fix bug on empty openmetrics scrape response

[ethan-lowman-dd]

What does this PR do?

It looks like #14445 introduced a bug that causes empty openmetrics scrapes to fail.

Without the fix, the added test fails as follows:

tests/test_openmetrics.py:110: in test_openmetrics_empty_response
    dd_run_check(check)
../datadog_checks_dev/datadog_checks/dev/plugin/pytest.py:228: in run_check
    raise Exception('\n'.join(exc_lines))
E   Exception:
E   Traceback (most recent call last):
E     File "/Users/ethan.lowman/go/src/github.com/DataDog/integrations-core/datadog_checks_base/datadog_checks/base/checks/openmetrics/v2/scraper.py", line 289, in parse_metrics
E       line_streamer = chain([next(line_streamer)], line_streamer)
E   StopIteration
E
E   The above exception was the direct cause of the following exception:
E
E   Traceback (most recent call last):
E     File "/Users/ethan.lowman/go/src/github.com/DataDog/integrations-core/datadog_checks_base/datadog_checks/base/checks/base.py", line 1135, in run
E       self.check(instance)
E     File "/Users/ethan.lowman/go/src/github.com/DataDog/integrations-core/datadog_checks_base/datadog_checks/base/checks/openmetrics/v2/base.py", line 64, in check
E       scraper.scrape()
E     File "/Users/ethan.lowman/go/src/github.com/DataDog/integrations-core/datadog_checks_base/datadog_checks/base/checks/openmetrics/v2/scraper.py", line 247, in scrape
E       for metric in self.consume_metrics(runtime_data):
E     File "/Users/ethan.lowman/go/src/github.com/DataDog/integrations-core/datadog_checks_base/datadog_checks/base/checks/openmetrics/v2/scraper.py", line 267, in consume_metrics
E       for metric in metric_parser:
E   RuntimeError: generator raised StopIteration

Motivation

Bug fix.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached
• If the PR doesn't need to be tested during QA, please add a qa/skip-qa label.

[codecov]

Codecov Report

Merging #14508 (6f7fa56) into master (6ddcc50) will increase coverage by 0.75%.
The diff coverage is 88.88%.

Flag	Coverage Δ
active_directory	100.00% <ø> (+17.64%)	⬆️
activemq_xml	82.31% <ø> (ø)
airflow	90.00% <ø> (ø)
amazon_msk	89.07% <ø> (ø)
ambari	85.75% <ø> (ø)
apache	95.08% <ø> (ø)
arangodb	98.21% <ø> (ø)
argocd	88.43% <ø> (ø)
aspdotnet	100.00% <ø> (+26.19%)	⬆️
avi_vantage	92.54% <ø> (ø)
azure_iot_edge	82.00% <ø> (ø)
boundary	100.00% <ø> (ø)
btrfs	82.91% <ø> (ø)
cacti	87.90% <ø> (ø)
calico	83.33% <ø> (ø)
cassandra_nodetool	93.16% <ø> (ø)
ceph	91.02% <ø> (ø)
cert_manager	77.41% <ø> (ø)
cilium	75.34% <ø> (+0.93%)	⬆️
cisco_aci	95.27% <ø> (ø)
citrix_hypervisor	87.50% <ø> (ø)
cloud_foundry_api	95.98% <ø> (+0.12%)	⬆️
cloudera	99.82% <ø> (ø)
cockroachdb	91.90% <ø> (ø)
consul	91.64% <ø> (ø)
coredns	94.54% <ø> (ø)
couch	95.19% <ø> (+0.48%)	⬆️
couchbase	84.28% <ø> (ø)
crio	89.79% <ø> (ø)
datadog_checks_base	89.66% <75.00%> (+0.34%)	⬆️
datadog_checks_dev	82.75% <ø> (+0.07%)	⬆️
datadog_checks_downloader	81.65% <ø> (ø)
datadog_cluster_agent	90.00% <ø> (ø)
ddev	99.16% <ø> (+0.52%)	⬆️
directory	96.42% <ø> (ø)
disk	89.16% <ø> (-2.15%)	⬇️
dns_check	93.90% <ø> (ø)
dotnetclr	91.39% <ø> (+12.90%)	⬆️
ecs_fargate	80.92% <ø> (ø)
eks_fargate	94.05% <ø> (ø)
elastic	91.91% <ø> (ø)
envoy	94.18% <ø> (ø)
etcd	93.96% <ø> (ø)
exchange_server	96.85% <ø> (+11.81%)	⬆️
external_dns	89.09% <ø> (ø)
fluentd	94.77% <ø> (ø)
foundationdb	78.50% <ø> (ø)
gearmand	78.26% <ø> (+1.24%)	⬆️
gitlab_runner	91.94% <ø> (ø)
glusterfs	80.09% <ø> (+0.92%)	⬆️
go_expvar	92.73% <ø> (ø)
gunicorn	92.10% <ø> (-0.76%)	⬇️
haproxy	95.13% <ø> (+0.16%)	⬆️
harbor	80.04% <ø> (ø)
hazelcast	92.39% <ø> (ø)
hdfs_datanode	89.74% <ø> (ø)
hdfs_namenode	86.72% <ø> (ø)
http_check	95.82% <ø> (+2.15%)	⬆️
ibm_ace	91.79% <ø> (ø)
ibm_db2	95.10% <ø> (ø)
ibm_i	81.95% <ø> (ø)
ibm_mq	91.37% <ø> (+0.13%)	⬆️
iis	95.00% <ø> (+37.60%)	⬆️
istio	77.43% <ø> (+0.55%)	⬆️
kong	87.56% <ø> (ø)
kube_apiserver_metrics	97.89% <ø> (ø)
kube_controller_manager	96.00% <ø> (ø)
kube_dns	95.97% <ø> (ø)
kube_metrics_server	94.87% <ø> (ø)
kube_proxy	96.80% <ø> (ø)
kube_scheduler	96.53% <ø> (ø)
kubelet	90.74% <ø> (ø)
kubernetes_state	89.18% <ø> (ø)
kyototycoon	85.96% <ø> (ø)
lighttpd	83.64% <ø> (ø)
linkerd	85.14% <ø> (+1.14%)	⬆️
linux_proc_extras	96.22% <ø> (ø)
mapr	82.70% <ø> (ø)
marathon	83.12% <ø> (ø)
marklogic	96.03% <ø> (ø)
mcache	93.50% <ø> (ø)
mesos_master	89.75% <ø> (ø)
mesos_slave	93.63% <ø> (ø)
mongo	96.63% <ø> (ø)
mysql	87.42% <ø> (+0.03%)	⬆️
nagios	89.01% <ø> (ø)
network	94.01% <ø> (+31.91%)	⬆️
nfsstat	95.20% <ø> (ø)
nginx	95.24% <ø> (+0.54%)	⬆️
nginx_ingress_controller	98.36% <ø> (ø)
openmetrics	98.02% <100.00%> (+0.06%)	⬆️
openstack	51.45% <ø> (ø)
openstack_controller	91.12% <ø> (ø)
pdh_check	95.65% <ø> (ø)
pgbouncer	91.33% <ø> (ø)
php_fpm	90.25% <ø> (+0.84%)	⬆️
postfix	88.04% <ø> (ø)
powerdns_recursor	96.65% <ø> (ø)
process	85.42% <ø> (+0.28%)	⬆️
prometheus	94.17% <ø> (ø)
proxysql	98.97% <ø> (ø)
pulsar	100.00% <ø> (ø)
redisdb	87.50% <ø> (ø)
rethinkdb	97.93% <ø> (ø)
riak	99.22% <ø> (ø)
riakcs	93.61% <ø> (ø)
sap_hana	91.37% <ø> (-0.27%)	⬇️
scylla	100.00% <ø> (ø)
silk	93.82% <ø> (ø)
singlestore	90.81% <ø> (ø)
snmp	84.55% <ø> (+0.04%)	⬆️
snowflake	96.47% <ø> (ø)
spark	93.63% <ø> (ø)
squid	100.00% <ø> (ø)
ssh_check	91.58% <ø> (ø)
statsd	87.36% <ø> (+1.05%)	⬆️
supervisord	92.30% <ø> (ø)
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temporal	100.00% <ø> (ø)
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varnish	84.39% <ø> (+0.26%)	⬆️
vault	95.53% <ø> (+0.57%)	⬆️
vertica	98.50% <ø> (ø)
voltdb	96.84% <ø> (ø)
vsphere	89.90% <ø> (+0.08%)	⬆️
win32_event_log	86.54% <ø> (+0.55%)	⬆️
windows_performance_counters	98.36% <ø> (ø)
windows_service	98.00% <ø> (ø)
wmi_check	92.91% <ø> (ø)
yarn	89.50% <ø> (ø)
zk	82.62% <ø> (+1.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[github-actions]

Test Results

     970 files       970 suites   6h 45m 37s ⏱️
  5 385 tests   5 309 ✔️      71 💤 2 ❌ 3 🔥
22 370 runs  18 711 ✔️ 3 654 💤 2 ❌ 3 🔥

For more details on these failures and errors, see this check.

Results for commit 6f7fa56.