You have the choice: you can use
The AspectJ Docs are similar to javadoc but contains also the AspectJ features like pointcuts, advices, ...
For some examples take a look at PatternTesting-Samples. The class patterntesting.sample.Config is an example how NullPointerExceptions can happen. It is also an example how you can use the @MayReturnNull and @NullArgsAllowed together with @NotNull.