def execute(workflow_service = nil)
      # If we're not given an explicit workflow service for this execution
      # request, use the one defined when we were created.
      workflow_service = @service if workflow_service.nil?
      # If we still have a nil workflow_service, go home.
      fail(IOError, ERR[:no_workflow_service_defined]) if workflow_service.nil?
      # Make sure we didn't forget any required parameters
      verify_parameters
      # Let's get this thing running!
      @execution_id = workflow_service.execute_workflow(@id, input_parameter_json)
    end
def execute(workflow_service = nil)
      # If we're not given an explicit workflow service for this execution
      # request, use the one defined when we were created.
      workflow_service = @service if workflow_service.nil?
      # If we still have a nil workflow_service, go home.
      fail(IOError, ERR[:no_workflow_service_defined]) if workflow_service.nil?
      # Make sure we didn't forget any required parameters
      verify_parameters
      # Let's get this thing running!
      @execution_id = workflow_service.execute_workflow(@id, input_parameter_json)
    end
Execute this workflow
 @param [VcoWorkflows::WorkflowService] workflow_service
 @return [String] Workflow Execution ID