Profiling pprof converter is raising exception when sorting _locations

[Truja]

Which version of dd-trace-py are you using?

0.54.0rc1

Which version of pip are you using?

21.3.1

Which version of the libraries are you using?

aiofiles==0.7.0
appdirs==1.4.4
appnope==0.1.2
asgiref==3.4.1
astroid==2.5
async-lru==1.0.2
attrs==21.2.0
Babel==2.8.0
backcall==0.2.0
black==19.10b0
boto3==1.18.51
botocore==1.21.51
cachetools==4.2.4
certifi==2021.5.30
chardet==4.0.0
charset-normalizer==2.0.6
click==8.0.1
colorama==0.4.4
commonmark==0.9.1
coverage==5.5
coveralls==3.2.0
datadog==0.42.0
ddtrace==0.54.0rc1
decorator==5.1.0
dnslib==0.9.16
dnspython==1.16.0
docker==5.0.0
docopt==0.6.2
dulwich==0.20.25
ecdsa==0.18.0b1
expiringdict==1.1.4
fastapi==0.68.1
Flask==2.0.1
greenlet==1.1.1
guppy3==3.1.1
h11==0.12.0
idna==3.2
importlib-metadata==4.8.1
inflect==5.3.0
iniconfig==1.1.1
ipython==7.28.0
isort==5.5.4
itsdangerous==2.0.1
jedi==0.18.0
Jinja2==3.0.1
jmespath==0.10.0
launchdarkly-server-sdk==7.2.0
lazy-object-proxy==1.6.0
localstack==0.12.17.5
localstack-client==1.24
localstack-ext==0.12.17
lxml==4.6.3
MarkupSafe==2.0.1
matplotlib-inline==0.1.3
mccabe==0.6.1
microservice-python==4.1.7
packaging==21.0
parso==0.8.2
pathspec==0.9.0
pbr==5.6.0
pexpect==4.8.0
pickleshare==0.7.5
pluggy==1.0.0
prompt-toolkit==3.0.20
protobuf==3.18.0
ptyprocess==0.7.0
py==1.10.0
pyaes==1.6.1
pyasn1==0.4.8
pydantic==1.8.2
Pygments==2.10.0
pylint==2.6.0
pylint-ext==0.4.0
Pympler==0.9
pyparsing==3.0.0rc1
pyRFC3339==1.1
pytest==6.2.5
pytest-asyncio==0.15.1
pytest-black==0.3.12
pytest-cov==2.10.1
pytest-env==0.6.2
pytest-isort==2.0.0
pytest-timeout==1.4.2
pytest-watch==4.2.0
python-dateutil==2.8.2
python-jose==3.3.0
python-multipart==0.0.5
pytz==2021.1
PyYAML==5.4.1
raven==6.10.0
regex==2021.8.28
requests==2.26.0
requests-mock==1.8.0
rich==10.10.0
rsa==4.7.2
s3transfer==0.5.0
semver==2.13.0
sentry-sdk==1.4.1
six==1.16.0
SQLAlchemy==1.4.23
starlette==0.14.2
stevedore==3.4.0
tabulate==0.8.9
tenacity==8.0.1
toml==0.10.2
traitlets==5.1.0
typed-ast==1.4.3
typing-extensions==3.10.0.2
urllib3==1.26.7
uvicorn==0.15.0
uvloop==0.16.0
watchdog==2.1.5
wcwidth==0.2.5
websocket-client==1.2.1
Werkzeug==2.0.1
wrapt==1.12.1
zipp==3.6.0

How can we reproduce your problem?

I am running my application with dd-trace-run and DD_PROFILING_ENABLED=true.

I started seeing the error after adding a threading.Timer() that calls that calls the same function some time ago, like described below.

I have a class that has a load() function which populates a cache. In the end of the load() function I call another function that starts a threding.Timer(), like:

    def load(self):
        # Do loading stuff

        # Set timer to reload data to cache
        self.start_cache_reload_timer()

    def start_cache_reload_timer(self):
        if self._timer is not None and self._timer.is_alive():
            self._timer.cancel()
        self._timer = threading.Timer(self._reload_period, self.load)
        self._timer.setName("CACHE_RELOAD_THREAD")
        self._timer.start()

My timer runs every 15 minutes and the profiling scheduler runs every 1 minute. The exception is raised when both match running time. However it does not happen every time that there is a match.

What is the result that you get?

I am seeing following exception in my log:

ERROR:ddtrace.profiling.scheduler:Unexpected error while exporting events. Please report this bug to https://github.com/DataDog/dd-trace-py/issues
Traceback (most recent call last):
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/ddtrace/profiling/scheduler.py", line 53, in flush
exp.export(events, start, self._last_export)
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/ddtrace/profiling/exporter/http.py", line 150, in export
profile = super(PprofHTTPExporter, self).export(events, start_time_ns, end_time_ns)
File "ddtrace/profiling/exporter/pprof.pyx", line 671, in ddtrace.profiling.exporter.pprof.PprofExporter.export
File "ddtrace/profiling/exporter/pprof.pyx", line 320, in ddtrace.profiling.exporter.pprof._PprofConverter._build_profile
TypeError: '<' not supported between instances of 'NoneType' and 'str'

What is the result that you expected?

No exception.