public Builder dockerImageRepository(String dockerImageRepository) {
            this.dockerImageRepository = (dockerImageRepository == null)
                    ? Optional.empty()
                    : Optional.of(DockerImage.fromString(dockerImageRepository));
            return this;
        }
Parameters for preparing an application. Immutable.

@author Ulf Lilleengen
configserver/src/main/java/com/yahoo/vespa/config/server/session/PrepareParams.java