added a compile-time dependency on the JSR 305 annotations. This is a
    [provided][maven_provided] dependency and does not need to be included in
    your build configuration, `.jar` file, or `.apk`. We use
    `@ParametersAreNonnullByDefault` and all parameters and return types are
    never null unless explicitly annotated `@Nullable`.

 *  **Warning: this release is source-incompatible for Kotlin users.**