Doc processing error with an object mapping and null value

While indexing GH archive dataset, I got this error:

2023-07-20T07:24:14.984Z  WARN quickwit_indexing::actors::doc_processor: error=ValueError("payload.pull_request.head.repo", "Expected an JSON Object, got null")

Here is the mapping:

doc_mapping:
  field_mappings:
    - name: id
      type: text
    - name: type
      type: text
      fast: true
    - name: actor
      type: object
      field_mappings:
      - name: login
        fast: true
        type: text
    - name: payload
      type: object
      field_mappings:
      - name: description
        type: text
        tokenizer: default
      - name: pull_request
        type: object
        field_mappings:
        - name: head
          type: object
          field_mappings:
            - name: repo
              type: object
              field_mappings:
                - name: description
                  type: text
                  tokenizer: default

I would expect that we just ignore the null value and still index the document.