None ("null") should not be encouraged in sequences ("arrays")

[Oberon00]

See the spec at https://github.com/open-telemetry/opentelemetry-specification/blob/v1.1.0/specification/common/common.md#attributes

null values SHOULD NOT be allowed in arrays. However, if it is impossible to
make sure that no null values are accepted
(e.g. in languages that do not have appropriate compile-time type checking),
null values within arrays MUST be preserved as-is (i.e., passed on to span
processors / exporters as null).

While Python cannot actually prevent None values, we at least can make sure that those who use mypy are made aware that they are adding an invalid value to an array by changing the Sequence[Optional[primitive]] to Sequence[primitive] in https://github.com/open-telemetry/opentelemetry-python/blob/v1.0.0/opentelemetry-api/src/opentelemetry/util/types.py#L23-L26

Actual code that is in place to accept None should continue to work as before.

[github-actions]

This issue was marked stale due to lack of activity. It will be closed in 30 days.

[eddyleelin]

I'd like to take a look into this as a good first issue! Would appreciate any help/direction for getting started on this.

[ocelotl]

@Oberon00 suggests that mypy users could use more information by changing the line pointed in the link. I would suggests getting somewhat familiar with what mypy is and does, @eddyleelin if you are not yet 👍