JENKINS-31217 Treat null as a default JDK name.

The intended change was just the POM change, and my other experiment
crept in.

add missing @Override annotations

Verify that *.properties do not have duplicated keys

Fix a NPE while trying to compare two data bound beans with null Iterable field.

Iterable field.

Another random failure

AbstractItem.java: replace non-Javadoc comment

Eclipse places "non-Javadoc" comments on methods that override methods
from supertypes, but these are nonstandard.  This change replaces this
comment with the standard Javadoc convention for this case.

[JENKINS-26270] Added "lastCompletedBuild" to permalinks.