Lots of nullable-annotated methods don't explain what conditions make them nullable

[ZacSweers]

This is super confusing to develop against as it's sort of guessing what could be causing this.

[EricKuck]

I'd like to get this fixed up ASAP, but I guess I'm not sure how documentation for that typically works. Were you thinking something like this?

    /**
     * Returns the host Activity of this Controller's {@link Router}. Will return null if this 
     * Controller has not yet been attached to an Activity or if the Activity has been destroyed.
     */
    @Nullable
    public final Activity getActivity() {
        return router != null ? router.getActivity() : null;
    }

[ZacSweers]

Yep that looks reasonable!

[PaulWoitaschek]

Javadoc would be like

  /**
   * @return the host Activity of this Controller's {@link Router} or {@code null} if this
   * Controller has not yet been attached to an Activity or if the Activity has been destroyed.
   */
  @Nullable
  public final Activity getActivity() {
    return router != null ? router.getActivity() : null;
  }

[EricKuck]

Thanks @PaulWoitaschek! I'll try to knock this out fast for the next release.