In ubuntu 16.04 the default monitrc includes "include /etc/monit/conf-enabled/*" at the end of the file. This is a great idea to optionally add configuration to this directory.
The problem is, if this one directory is empty, monit will raise the following failure message:
# monit summary /etc/monit/monitrc:300: Include failed -- Success '/etc/monit/conf-enabled/*'
In my opinion this shouldn't happen. Those kind of includes are meant to be optional and should raise an error. In our case we use a second directory to store most of our configs, but we would like to leave the OS directory in there, in case we like to include one of those configs.