Rebuild plugin (v1.21+) provides an extension point for other plugins to register their customized parameter value.

Gerrit Trigger has such a customized parameter (Base64EncodedStringParameter), however, no extension point is provided by Gerrit Trigger.
If we rebuild a parametrized build with such a parameter from Gerrit Trigger, the parameter page will be broken.

We need such a functionality in Gerrit Trigger to have it work well with Rebuild plugin.