This method can be used to alter the descriptor read in. It can also
add descriptors, or remove the descriptor (by returning null).
Any alterations made to the descriptor passed in will remain in effect.
serviceLocator - the ServiceLocator being populated. Will not be null
descriptorImpl - The descriptorImpl read from some external source. This
processor can modify this descriptor fully
The descriptor to be added to the system. If this returns null
then the descriptorImpl passed in will NOT be added to the system. Implementations
may return the descriptor passed in, but do not have to. The descriptor added to
the system will be the one returned from this method