The command syntax you have shown above is actually incorrect. Have you typed it completely by hand?
Issuing the command you have shown gives you a proper error:
There is also a dash missing in front of the first 'key' attribute. So this command should work:
roo> database properties set -key database.url --key jdbc:mysql://localhost/testdb
You must specify option 'value' for this command
Tab completion in the shell should help you avoid this in future .
roo> database properties set --key database.url --value jdbc:mysql://localhost/testdb