Github poller does not work as expected

[jianliang00]

I'm trying to use the git repository poller in my own CDS services to get events from Github. After the services get running correctly, I make some changes in my repository on Github, but I can't find any events triggering my workflows.
Here's part of my workflow configuration and I'm sure the vcs service can access my repository:

hooks:
  test1:
  - type: Git Repository Poller
    config:
      payload: '{}'

I tried to debug the source code and found that the key problem is the following line：

The function mapstructure.Decode did not decode the event payload correctly. Instead, it leaves all the fields of MergeRequest struct empty.

Here's the value of variable i. Notice that the field state of merge_request has the value open

And Here's the value of variable e. The field State of MergeRequest along with other fields are all empty

I believe there shouldn't be such a blatant bug in Mapstructure, yet I'm perplexed as to why such a situation arises.

Can anyone give me some help?