Annotations

[sharwell]

• Move @NotNull and @Nullable to their own artifact
• Add NullUsageProcessor annotation processor to validate correct usage (at compile time) of the annotations in many scenarios

The following is a list of the scenarios analyzed and reported by this processor during the build process.

• Error: an element is annotated with both @NotNull and @Nullable.
• Error: an method which returns void is annotated with @NotNull or @Nullable.
• Error: an element with a primitive type is annotated with @Nullable.
• Error: a parameter is annotated with @NotNull, but the method overrides or implements a method where the parameter is annotated @Nullable.
• Error: a method is annotated with @Nullable, but the method overrides or implements a method that is annotated with @NotNull.
• Warning: an element with a primitive type is annotated with @NotNull.
• Warning: a parameter is annotated with @NotNull, but the method overrides or implements a method where the parameter is not annotated.
• Warning: a method is annotated with @Nullable, but the method overrides or implements a method that is not annotated.