I have no idea why this started happening, but my SDKMAN stopped working and only displays the following message for whatever package I want to list, install, or use.
$ sdk list java
Stop! java is not a valid candidate.
$ sdk install java
Stop! java is not a valid candidate.
$ sdk use java 8u131
Stop! java is not a valid candidate.
Just typing sdk list works, though. But I can't do anything. My .bash_profile contains the following:
export JAVA_HOME=$(/usr/libexec/java_home)
export SDKMAN_DIR="/Users/myusername/.sdkman"
[[ -s "/Users/myusername/.sdkman/bin/sdkman-init.sh" ]] && source "/Users/myusername/.sdkman/bin/sdkman-init.sh"
The problem was on the server side. Something to do with SDKMAN's Candidates API. As pointed out in the GitHub issue, you can get over the problem using the following command:
sdk flush candidates
Make sure to restart your terminal after that.