How do I query a null date inside an array in elasticsearch?

In an elasticsearch query I am trying to search Document objects that have an array of approval notifications. The notifications are considered complete when dateCompleted is populated with a date, and considered pending when either dateCompleted doesn't exist or exists with null. If the document does not contain an array of approval notifications then it is out of the scope of the search.

I am aware of putting null_value for field dateCompleted and setting it to some arbitrary old date but that seems hackish to me.

I've tried to use Bool queries with must exist doc.approvalNotifications and must not exist doc.approvalNotifications.dateCompleted but that does not work if a document contains a mix of complete and pending approvalNotifications. e.g. it only returns document with ID 2 below. I am expecting documents with IDs 1 and 2 to be found.

How can I find pending approval notifications using elasticsearch?

PUT my_index/_mapping/Document

 "properties" : {
  "doc" : {
    "properties" : {
      "approvalNotifications" : {
        "properties" : {
          "approvalBatchId" : {
            "type" : "text",
            "fields" : {
              "keyword" : {
                "type" : "keyword",
                "ignore_above" : 256
              }
            }
          },
          "approvalTransitionState" : {
            "type" : "text",
            "fields" : {
              "keyword" : {
                "type" : "keyword",
                "ignore_above" : 256
              }
            }
          },
          "approvedByUser" : {
            "type" : "text",
            "fields" : {
              "keyword" : {
                "type" : "keyword",
                "ignore_above" : 256
              }
            }
          },
          "dateCompleted" : {
            "type" : "date"
          }
        }
      }
    }
  }
}

Documents:

{
    "id": 1,
    "status": "Pending Notifications",
    "approvalNotifications": [
        {
            "approvalBatchId": "e6c39194-5475-4168-9729-8ddcf46cf9ab",
            "dateCompleted": "2018-11-15T16:09:15.346+0000"
        },
        {
            "approvalBatchId": "05eaeb5d-d802-4a28-b699-5e593a59d445",
        }
    ]
}

{
    "id": 2,
    "status": "Pending Notifications",
    "approvalNotifications": [
        {
            "approvalBatchId": "e6c39194-5475-4168-9729-8ddcf46cf9ab",
        }
    ]
}

{
    "id": 3,
    "status": "Complete",
    "approvalNotifications": [
        {
            "approvalBatchId": "e6c39194-5475-4168-9729-8ddcf46cf9ab",
            "dateCompleted": "2018-11-15T16:09:15.346+0000"
        },
        {
            "approvalBatchId": "05eaeb5d-d802-4a28-b699-5e593a59d445",
            "dateCompleted": "2018-11-16T16:09:15.346+0000"            
        }
    ]
}

{
    "id": 4
    "status": "No Notifications"
}