no highlights with a highlight prefix query and FVH when no match found

[v1r]

Following this issue: #25088

Elasticsearch version: 5.4.0 and 5.4.1
JVM version: 1.8
OS version : Windows 7

No highlights returned using a prefix in a highlight_query when a document attribute has an empty value or no match found

Steps to reproduce:

Create the following index

PUT foo
{
  "mappings": {
    "blogpost": { 
      "properties": { 
        "title": { "type": "text", "term_vector": "with_positions_offsets"}, 
        "description":  { "type": "text", "term_vector": "with_positions_offsets"  }
      }
    }
  }
}

Add a new document, notice description is empty (no match for 'sq' string).

PUT foo/entry/1
{
  "title": "SQ05_H04_WorldTour test",
  "description": ""
}

Run the following query to highlight the string containing 'sq'.

GET foo/_search
{
   "query":{
      "match_all":{ }
   },
   "highlight":{
      "fields":{
         "title":{
            "number_of_fragments":10,
            "type":"fvh",
            "highlight_query":{
               "prefix":{
                  "title":"sq"
               }
            }
         },
         "description":{
            "number_of_fragments":10,
            "type":"fvh",
            "highlight_query":{
               "prefix":{
                  "description":"sq"
               }
            }
         }
      },
      "require_field_match":false
   }
}

The result as expected highlights the string containing 'sq'

{
  "took": 0,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 1,
    "max_score": 1,
    "hits": [
      {
        "_index": "foo",
        "_type": "entry",
        "_id": "1",
        "_score": 1,
        "_source": {
          "title": "SQ05_H04_WorldTour test",
          "description": ""
        },
        "highlight": {
          "title": [
            "<em>SQ05_H04_WorldTour</em> test"
          ]
        }
      }
    ]
  }
}

Lets re-execute the same query, but this time we change the order of fields..

GET foo/_search
{
   "query":{
      "match_all":{ }
   },
   "highlight":{
      "fields":{
         "description":{
            "number_of_fragments":10,
            "type":"fvh",
            "highlight_query":{
               "prefix":{
                  "description":"sq"
               }
            }
         },
         "title":{
            "number_of_fragments":10,
            "type":"fvh",
            "highlight_query":{
               "prefix":{
                  "title":"sq"
               }
            }
         }
      },
      "require_field_match":false
   }
}

Surprisingly, no highlighs returned..

{
  "took": 0,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 1,
    "max_score": 1,
    "hits": [
      {
        "_index": "foo",
        "_type": "entry",
        "_id": "1",
        "_score": 1,
        "_source": {
          "title": "SQ05_H04_WorldTour test",
          "description": ""
        }
      }
    ]
  }
}

is this is a bug? same behavior in 2.x

[v1r]

This is also true for multi terms query like wildcard, regexp