This has caught me out on a few occasions:
When trying to run the
update-database command in Package manager within visual studio , i repeatedly got the error:
Join-Path : Cannot bind argument to parameter 'Path' because it is null.
In this instance, i was not pointing the "Default Project" to the data project that I was using.
Simply choose it from the options within the package manager window and re-run the update command.
This should solve the problem.