Answer node

[KennyHuangChina]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

I was try to build my work-flow, and when I try to add an "answer node" in my work-flow, I got something wired, I can't find the "answer node" in list, like the following picture shows

I'm quite curious. Where has my "answer node" gone?

2. Additional context or comments

I've test in both 0.14.2 & 0.15.1, what's wrong with it?