d96550898f
Prior to this commit, calls to getAllow would fail is setAllow was set
to an EmptyCollection right before.
java.lang.IllegalArgumentException: No enum constant
org.springframework.http.HttpMethod
This commit fixes this by testing the header value for an empty value
before trying to use it to get a value from the Enum.
Issue: SPR-11917
(cherry picked from commit 9054f4f)