Special Case Product Bundle Relationships

When relating Products to Product Bundles it is
necessary to provide an index (sequence) for the
Products.  Without this index only the most
recently related Product is visible on a Quote.
Reasonable Defaults

If attempting to retrieve fields from a non-existent
Sugar Entry the return value in entry_list is falsey.
All fields in SugarEntries default to blank strings,
so when this empty response is received all fields
that were requested can be set blank.