Git error when running without --from option

[ciaranmcnulty]

Steps to reproduce:

1. check out phpspec/phpspec
2. add this tool to composer requires and update
3. run vendor/bin/roave-backward-compatibility-check

Error:

[Symfony\Component\Process\Exception\ProcessFailedException]                     
  The command "'git' 'rev-parse' ''" failed.                                       
                                                                                   
  Exit Code: 128(Invalid exit argument)

The input parameter --from is optional so its default value is NULL. this is explicitly cast to a string '' in AssertBackwardsCompatible::parseRevisionFromInput, but the implementation of GitParseRevision then builds a the CLI with an empty string, which breaks as above

[ciaranmcnulty]

oh I see the problem, will PR

[Ocramius]

Handled in #73