Quote if necessary Etags set with ResponseEntity builder API [SPR-13378]

[spring-projects-issues]

Brian Clozel opened SPR-13378 and commented

Using ResponseEntity's builder API like the following throws an IllegalArgumentException because the ETag is not quoted "foo" nor a weak ETag W/"foo":

ResponseEntity<Void> responseEntity = ResponseEntity.ok().eTag("foo").build();

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Affects: 4.2 GA

Referenced from: commits 88405be