was: Exception when saving job config due to empty Classpath entry

The following issue looks caused for the "minimum" of the successor repeatableProperty are inherit from the ancestor repeatableProperty.
Promoted-build always displays more than 1 entry, and every properties with entries under promoted-build are forced that rule.

Steps to reproduce:

1. Create a new freestyle project
2. Add a promotion process
3. Add Groovy Postbuild action to the new promotion process
4. Save the job config
5. Configure the job again
6. Notice there's now a "Classpath entry" that wasn't there initially.
7. Try to save the job again without any changes gives the following exception:

java.net.MalformedURLException: JENKINS-37599: empty classpath entries not allowed
at org.jenkinsci.plugins.scriptsecurity.scripts.ClasspathEntry.pathToURL(ClasspathEntry.java:62)
at org.jenkinsci.plugins.scriptsecurity.scripts.ClasspathEntry.<init>(ClasspathEntry.java:57)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at

It would be best if the plugin did not add an additional classpath entry if it is not needed/desired.