Incorrect unit name in .bkp instantiation causes a panic

The following .bkp file causes a panic:

unit basic where
  signature Basic where

unit main where
  dependency basic [ Basic = nonsense:Nonsense ]

ghc.exe --backpack Error1.bkp
[1 of 2] Processing basic
  [1 of 1] Compiling Basic[sig]       ( basic\Basic.hsig, nothing ) [Flags changed]
[2 of 2] Processing main
panic! (the 'impossible' happened)
  GHC version 9.3.20210928:
        no package name
CallStack (from HasCallStack):
  error, called at compiler\GHC\Driver\Backpack.hs:647:32 in ghc:GHC.Driver.Backpack

It would be better to catch the problem early and report an appropriate error message.