protected String addDependency(FunctionalTaskItem dependency) {
        Objects.requireNonNull(dependency);
        return this.taskGroup().addDependency(dependency);
    }
protected String addDependency ( FunctionalTaskItem dependency ) { Objects . requireNonNull ( dependency ) ; return this . taskGroup ( ) . addDependency ( dependency ) ; }
Add a dependency task item for this model.

@param dependency the dependency task item.
@return key to be used as parameter to taskResult(string) method to retrieve result the task item