On ingesting TIPPs from GOKb only attempt to create a coverage statement in Local KB if there is a coverage statement in GOKb

Currently on harvesting GOKb, many errors of the type:

Property [startDate] of class [class org.olf.dataimport.erm.CoverageStatement] cannot be null

are logged. This is because there are many TIPPs (equivalent to PCI) in GOKb that lack coverage. This does not stop the resource being added to the local KB, but it does cause an error when trying to create a coverage statement (as these must have a startDate).

It's valid for a PCI to not have any coverage at all, so when the GOKb TIPP does not have any coverage statement, then no attempt to create coverage should be made for PCI