After guidance on submitting patches for potential bugs and deprecations

What are the rules for fixing potential bugs or replacing deprecated API's in code I may be working on?

As an example, say I find instances where there is null dereferencing where it is observed an NPE is likely to be thrown where a prior null check is used. Should I create an issue as ENHANCEMENT and provide a patch?

What about deprecated NetBeans API's where a replacement is available and often the IDE has a suggested fix. Should I also create an ENHANCEMENT and submit the patch?

And what about simpler enhancements, like
- `Collection/Map.size() == 0` -> isEmpty()
- manual array-copying -> System.arraycopy
- unchecked conversions

I'm more than willing to help out with these sorts of things, especially on modules I use all the time.