[Issue #897] Flush on unbatched producer panics

[flowchartsman]

Fixes #897

Am not certain if this is the right place or behavior, so opening it up for comments. It might be that it is fine to panic on a Flush() to a non-batching producer, provided it's explicitly documented, but probably not. It's worth noting that it worked in the past, which is how I ran into the issue in the first place, since I left an errant Flush() call behind in some tests after disabling batching on a producer.

Master Issue: #

Motivation

No one wants a panic, especially one that is undocumented.

Modifications

nil check.

Verifying this change

• Make sure that the change passes the CI checks.

I've included tests.

Documentation

Since this issue would normally cause a panic, it's probably not necessary to document anything special, especially considering that a similar check is made elsewhere throughout the code. If requested, I can add a comment to the Flush() Godoc mentioning that it is a no-op for non-batching producers.

[pgier]

LGTM, but maybe the formatting changes should be a separate PR since they are not related to the bug.

[shibd]

@flowchartsman Can you remove invalid formatting changes?

[dimovnike]

it might be that it is fine to panic on a Flush() to a non-batching producer

may be it is but it is still better if an error is returned, not panic.

[flowchartsman]

This issue was duplicated by #1064 (I guess no one searches issues any more) and fixed by #1065. Closing this as superceded.