Google has a nice library to check for common Java coding errors during build-time. It's called Error Prone:
We should enable this on our codebase, as it provides useful tips to developers when they made a common mistake in their code (and links them to resources on how to fix it).
I've been working today on enabling it on "master" and it's founds several minor bugs in our code that are worth resolving. PR coming shortly with more details