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 cannot find a contributing item that links with the primary item. There are three possible behaviors:

error

If there is no contributing item found, a RuntimeException is thrown.

default

If there is no contributing item found, the default value for that property in the contributing item descriptor is returned. If there is no default value, null is returned

null

If there is no contributing item found, null is returned automatically.