Populate tasks in internal workflowTask and activityTask entities for empty polls

[shijiesheng]

What changed?
ensure task field is populated in workflowTask and activityTask for empty polls.

Why?

Task response even with empty task contains information like AutoConfigHint, which is needed for poller auto scaler

How did you test it?

Unit Test

Potential risks

[neil-xie]

why can not we reuse the autoConfigHint inside task(PollForDecisionTaskResponse) here? I'm assuming task != nil will mess up the logic somewhere else

[shijiesheng]

I haven't tried. But the field is widely used in many different places. Breaking the Nilness assumption might mess it up.

[taylanisikdemir]

I don't think we need the new field. It's a redundant information and requires each instantiation of workflowTask/activityTask to fill it based on the response.
Instead expose a helper function such as:

func (wt *workflowTask) GetAutoConfigHint() *s.AutoConfigHint {
   if wt.task == nil {
     return nil
  }
  return wt.task.GetAutoConfigHint()

Less code to write and maintain.

[shijiesheng]

yeah, I checked carefully. We can populate this task field for empty polls. Thus I've changed the title as well.

[taylanisikdemir]

let's also add nil cases

[shijiesheng]

It's actually not possible for client to return nil, nil for both response and error so I'll skip the test