The null-contributing-item-policy attribute determines how the composite repository should behave if it tries to get the value of a property from a contributing repository item, but the repository is unable to find a contributing item that links with the primary item. There are three possible behaviors:
error
If there is no contributing item found, then a RuntimeException is thrown.
defaultIf there is no contributing item found, then the default value for that property in the contributing item descriptor is returned. If there is no default value, then null is returned
null
If there is no contributing item found, then null is returned automatically.
