Bug: getting location on Maven 3 model explodes

[cstamas]

Affected version

master

Bug description

Model location explodes, doing this on Maven 3 (in Maven 3 plugin) d.getLocation(null) causes that below.

Caused by: java.lang.NullPointerException: Cannot invoke "Object.hashCode()" because "pk" is null
    at java.util.ImmutableCollections$MapN.probe(ImmutableCollections.java:1328)
    at java.util.ImmutableCollections$MapN.get(ImmutableCollections.java:1242)
    at org.apache.maven.api.model.Dependency.getLocation(Dependency.java:244)
    at org.apache.maven.model.Dependency.getLocation(Dependency.java:178)

[gnodet]

In Maven 3, xx.setLocation(null, loc) is a no-op, so that xx.getLocation(null) always return null. Even though the javadoc on InputLocationTracker clearly indicates null keys are not supported on getLocation and setLocation.

We need to fix Maven 4 to assert the location parameter is non-null in InputLocationTracker.getLocation, and complete the javadoc for that org.apache.maven.api.model.InputLocationTracker class.