Adding tests to repro null index bug when empty index file exists.
Fixing empty index bug.
Using Before annotation to create ZincRepoIndexWriter.
Removing unncessary assertions.
Removing tests.
Simplifying ZincRepoIndexWriter
ZincRepoIndexWriter: checking for null in the caller instead.
Merge pull request #20 from mindsnacks/fixing_null_zinc_repo_index_bug

[Final] Fixing null zinc repo index bug.