Support skip nil for cache fetch

[Martin91]

Summary

Provide a skip_nil setting for cache store. According to our cases, we need to cache some results retrieved from external services with 1 day expiration time, but if they are down with some accidental reasons, nil result will be cached whole day, instead, we hope not to cache that result, so we can always retry retrieving and it can cache expected result again once the services come back normal.

I have added one more spec for this setting and it ensures not to break existed behaviours, I also updated the documentation for #fetch method.

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[Martin91]

@sgrif @maclover7 I saw some build failures in ci but I think they are not related to my PR, should I pay attention to or am responsible for them?

[maclover7]

@Martin91 nope, master is failing right now. will be green again once #25436 is merged in.

[Martin91]

Ok, glad to sound that
Jon Moss notifications@github.com于2016年6月20日 周一上午4:47写道：

@Martin91 https://github.com/Martin91 nope, master is failing right
now. will be green again once #25436
#25436 is merged in.

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[Martin91]

I wonder if anyone has any opinion on this PR?

[schneems]

This seems fine. Can you fix the conflicts?

[Martin91]

@schneems Sure.

[Martin91]

@schneems I have rebased the branch and resolved the conflicts.

[schneems]

Tests are failing, can you take a look. Also I’ll need a change log entry for this.

We are getting close, thanks for your work here!

[Martin91]

@schneems I have added a change log entry and it seems that all tests have passed.

[schneems]

Thanks!

[rlue]

This feature was announced here as a feature of Rails 5.2.1, but it appears to be absent from the 5-2-stable branch—have I missed something? If not, is there any chance we could get it backported?

[kamilpp]

I confirm that skip_nil option is not present in Rails 5.2, despite it was announced so

[rafaelfranca]

It was not announced as part of 5.2. It was announced in the same email saying that 5.2.1 was released but nothing there say it is part of 5.2. Am I missing something?

[rlue]

Ah, so that's how it works! My mistake.

[leoplct]

How can I pass a boolean variable to force skipping the cache?
At the moment I can pass {force: true} but this will cache results. I am looking to not read/save cache where some conditions applies.