Made Nullables in EPA Database Types to better reflect the database.

Added Tests
Fixed a bug where PriceListSetFilters would successfully complete because of a modification to a member of the objects used in a collection.

Minor performance optimizations. (They might save you a couple nanoseconds though).
Fixed an occurance of a nullable value which caused random errors because it wasn't actually suppose to be nullable
Put a check in PriceListFilters so that any inconsistency with the priceListFilters and the PriceListId would should throw an error.
Change primary keys of PriceAgreement Adjustments

Fixed a bug which could cause searching for Price Agreements to infinitely loop