javagit/src/main/java/edu/nyu/cs/javagit/client/cli/CliGitCheckout.java
public GitCheckoutResponse checkout(File repositoryPath, Ref branch) throws JavaGitException,
            IOException {
        return checkout(repositoryPath, null, branch);
    }
public GitCheckoutResponse checkout(File repositoryPath, Ref branch) throws JavaGitException,
            IOException {
        return checkout(repositoryPath, null, branch);
    }
Checks out a branch from the git repository with a given branch name.