Control File: empty dependency name
Many fields accept a list of dependencies (Depends, Build-Depends, etc.). That list must define a set of names separated by commas. If two commas are written one after another, the dependency name is viewed as empty (This is a Debian thing, I would just ignore such... oh well!)
Also, defining a field without a list of dependencies can get you this error too, although in general an empty field is legal.
VALIDDepends: boost, qt, libqtcassandra
Conflicts: postfix,
INVALIDDepends: boost,, libqtcassandra