title: Best way to do a delete operation with GraphQL + graphene
body: <p>I'm struggling to get my Delete operation working.
  My Create, Read and Update are working fine, but a Delete has nothing to return.</p>
  
  <pre><code>class DeleteEmployeeInput(graphene.InputObjectType):
      """Arguments to delete an employee."""
      id = graphene.ID(required=True, description="Global Id of the employee.")
  
  
  class DeleteEmployee(graphene.Mutation):
      """Delete an employee."""
      employee = graphene.Field(
          lambda: Employee, description="Employee deleted by this mutation.")
  
      class Arguments:
          input = DeleteEmployeeInput(required=True)
  
      def mutate(self, info, input):
          data = utils.input_to_dictionary(input)
          #data['edited'] = datetime.utcnow()
  
          employee = db_session.query(
              EmployeeModel).filter_by(id=data['id'])
          employee.delete(data['id'])
          db_session.commit()
          #employee = db_session.query(
              #EmployeeModel).filter_by(id=data['id']).first()
  
          #return DeleteEmployee(employee=employee)
  </code></pre>
  
  <p>What is the best way to delete an entry?
  I assume I have to return an OK or an Error.</p>
  
  <p>When I run my mutation:</p>
  
  <pre><code>mutation {
    deleteEmployee (input: {
         id: "RW1wbG95ZWU6MQ=="
    }) 
  }
  </code></pre>
  
  <p>I get the error <code>Field \"deleteEmployee\" of type \"DeleteEmployee\" must have a sub selection."</code></p>
  
  <p>Note the commented out lines</p>