* Consistent license message for all the go files
* Fixing the last set of unconsistencies with the license headers
* Addressing PR review comments
* Fixing busy.go and busy_test.go license header
* MM-18167: fix KV* helpers error handling
Returning a `nil` `*model.AppError` does not make a `nil` `error`
interface. As a consequence, all of the KV* helper methods would always
appear to fail, even if the underlying API call was successful.
Fix this mismatch by explicitly assigning `appErr` in the helpers and
only ever returning a `nil` `error` interface. Extend unit tests to
achieve 100% coverage of the associated files.
In the long run, we must change all function signatures to return the
`error` interface instead of the abomination that is returning
`*model.AppError` today.
* Implement KVCompareAndDelete and KVCompareAndDeleteJSON
* Add tests for KVCompareAndDelete
* Update minimum server version
* Handle nil value on CompareAndSet so that it deletes it
* Fix comments
* Tweaks from PR comments
* Go back to deleted, err
* move kv helpers to helpers_kv*.go
* change KVGetJSON return signature
Return a boolean and an error, to clearly indicate if no value was found and thus no value unmarshalled into the target interface.
Also fix an issue with CompareAndSet to allow an oldValue of nil (i.e.
expected to be unset).
* add missing license
* tweak documentation
* document KVSetWithExpiryJSON minimum version
