IWF-124: Ignore empty output for collector

[longquanzheng]

Description

Before

After

Checklist

• Code compiles correctly
• Tests for the changes have been added
• All tests passing
• This PR change is backwards-compatible
• This PR CONTAINS a (planned) breaking change (it is not backwards compatible)

Related Issue

Closes #issue_number

[ktrops]

If the state doesn't have any output, then it'll be empty? I was using it to know what workflow execution completed. I guess the state id count could work for that.

[longquanzheng]

If the state doesn't have any output, then it'll be empty? I was using it to know what workflow execution completed. I guess the state id count could work for that.

waiting on workflow execution will still work, it doesn't rely on this.
What "maybe" a small breaking change is that the output of the waitForWorkflowCompletion won't have the stateId/stateExecutionId anymore for those who completing the "threads".

[stevo89519]

What "maybe" a small breaking change is that the output of the waitForWorkflowCompletion won't have the stateId/stateExecutionId anymore for those who completing the "threads".

Is this a concern we need to address?

[longquanzheng]

What "maybe" a small breaking change is that the output of the waitForWorkflowCompletion won't have the stateId/stateExecutionId anymore for those who completing the "threads".

Is this a concern we need to address?

I think we can ignore.
The issue is only in theory but not practical.
We have this API in java SDK https://github.com/indeedeng/iwf-java-sdk/blob/055f2836ebc375b569b28ea7b45318b847c9ea2b/src/main/java/io/iworkflow/core/Client.java#L427

getComplexWorkflowResultWithWait it will return all the completed states even the completion output is empty. So in theory, if someone rely on this in production, it's a breaking changes. But I don't think anyone would do that in practile (I don't see anyone using this API in Indeed, or samples at all, and I doubt any OSS users even aware of this API).

cc @lwolczynski

[lwolczynski]

Continuing in !524