Add missing @Nullable in SettableListenableFuture

[jensdietrich]

Add @Nullable to return type of org.springframework.util.concurrent.SettableListenableFuture::get()

Supporting test traces illustrating the use of null in actual program behaviour:

org.springframework.util.concurrent.SettableListenableFuture::get:119
org.springframework.util.concurrent.SettableListenableFutureTests::nullIsAcceptedAsValueToSet:223

This issue has been found by an automated analysis and confirmed by manual inspection.
A description of the analysis performed can be found here: (https://github.com/jensdietrich/null-annotation-inference).

[jensdietrich]

I just realised that checkstyle expects the annotation to be on a separate line. I can withdraw this and create another PR to comply with this rule if required.

[sbrannen]

I just realised that checkstyle expects the annotation to be on a separate line. I can withdraw this and create another PR to comply with this rule if required.

No need to create a new PR.

Whenever you need to make a change to an existing PR, you can simply push another commit to the branch for the PR.

In this particular case, we can take care of it for you.

By the way, SettableListenableFuture#get(long, TimeUnit) is also missing a @Nullable declaration, but I'll take care of that.

[jensdietrich]

thanks @sbrannen for accepting the change. I have a significant number of other missing @Nullable annotations inferred by the tool we have developed (part of our research at Victoria University of Wellington, with support from Oracle Labs), and I wonder what the best way is to get this actioned. I could create more PRs, but I wonder what a good level of granularity would be as some of them affect many classes. I picked this one as a pilot. An alternative would be perhaps via an issue, where I could post the reports generated with details about the inferred annotations including supporting provenance, but committers would have to do the actual changes. BTW, the tool can also make changes to the source code. Any advice is highly appreciated.

module	fields	params	returns	all
spring-beans	1 (1)	75 (47)	7 (7)	83 (51)
spring-context	1 (1)	50 (34)	16 (15)	67 (47)
spring-core	0 (0)	39 (22)	1 (1)	40 (23)
spring-orm	0 (0)	17 (13)	4 (4)	21 (14)
spring-oxm	0 (0)	3 (2)	2 (1)	5 (3)
spring-web	19 (8)	164 (76)	25 (19)	208 (97)
spring-webmvc	0 (0)	109 (59)	44 (36)	153 (89)

Missing @nullable Annotations Detected by Module and Type of Annotated Element. The numbers in brackets are the numbers of classes affected. See https://github.com/jensdietrich/null-annotation-inference for the methodology used.