The type signature for `get_metrics_data()` says return type should never be None (but it can be)

[ocelotl]

          The type signature for `get_metrics_data()` says return type should never be None https://github.com/open-telemetry/opentelemetry-python/blob/f1bebffbc429b4e9b3a77eb61f5aa2a7651c4beb/opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/export/__init__.py#L405-L407

Originally posted by @aabmass in #3978 (comment)

[aabmass]

When can it be None @ocelotl ? Would appreciate a link to the broken code or repro

[Ali-Alnosairi]

Can I take this ?

[xrmx]

@Ali-Alnosairi no need to ask on 6 different issues, pick one and eventually open a PR.

[Ali-Alnosairi]

Hi @ocelotl , @lzchen,
How to reproduce the issue ?
I need to reproduce the issue , so I can fix it
would someone help please!

[emdneto]

Hey @Ali-Alnosairi:
Some issues will require discovery/code reading to determine what to do. Not all issues have an easy repro snippet that you can use to reproduce. In that case, I suggest you read the thread and understand the discussion. If you take a look, you will notice there is a test asserting that metrics_data is None.

[ocelotl]

When can it be None @ocelotl ? Would appreciate a link to the broken code or repro

There are a couple of ways this can happen, PTAL in #4190