@RequestParam Optional<List<?>> not handling multiple params of the same name correctly [SPR-15857]

[spring-projects-issues]

Cole Snodgrass opened SPR-15857 and commented

A @RequestParam Optional<List<String>> param will only return the first element if the param is specified multiple times in the query-string.

e.g.
?param=a,b,c will return the expected value but ?param=a&param=b&param=c will not

This is inconsistent with @RequestParam List<String>> param behavior. I have a workaround by using @RequestParam(required = false) List<String> param but this is not ideal.

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Affects: 4.3.9

Reference URL: https://gist.github.com/cole-snodgrass/1e6270d4007841af8cff082e2aac8316

Issue Links:

• Request params Optional<List<String> and List<String> are inconsistent [SPR-15676] #20235 Request params Optional<List and List are inconsistent ("duplicates")