Cabal refuses to install when the "License" field is incorrect, without a clear message

I tried to install a package with

```
license-file: ""
```

in the .cabal file and got the messages:

```
> cabal install
[...]
setup-Simple-Cabal-1.22.5.0-x86_64-windows-ghc-7.10.3.exe: : does not exist
[...]
cabal: Error: some packages failed to install:
Macbeth-lib-0.0.9 failed during the final install step. The exception was:
ExitFailure 1
```

Giving the command:

```
cabal -j1 install
```

leads to the message:

```
Warning: The 'license-file' field refers to the file '' which does not exist.
```

which is much clearer, but the package is still not being installed.
After adding the proper file name for the license file to the .cabal file, the package was installed.