Use Optional instead of @Nullable
Update based on review comments
Merge branch 'tm-import' of github.com:zanata/zanata into tm-import

Conflicts:
	zanata-war/src/main/java/org/zanata/tmx/TransMemoryAdapter.java
	zanata-war/src/main/java/org/zanata/webtrans/client/ui/TMMergeForm.java
	zanata-war/src/main/java/org/zanata/webtrans/server/rpc/GetTransMemoryHandler.java
Update based on review comments