TermQuery formation when searching a JSON object against a non analyzed string

[neham (Neha)]

I have a mapping like

{:assignee {:type "string"
            :include_in_all false
            :index "not_analyzed"
            :null_value "unassigned"}}

If I want to search a document with assignee as "neha" my query would be
{"query": {"bool": {"must": [{"term": {"assignee":"neha"}}]}}}
This works perfectly fine.
What I want to understand is when I pass an JSON object other than string as assignee to terms query, the query execution shows that it is being converted into 4 termQueries for example:
{"query": {"bool": {"must": [{"terms": {"assignee": [{"profile_id":"neha"}]}}]}}}
Following TermQueries are being used

1. assignee:profile_id
2. assignee:neha
3. assignee:{
4. assignee:}
   As a result ES still returns search hits because of the second TermQuery. Here assignee is a not analyzed string. Then why are 4 TermQueries being formed here?
   Is this intentional? If not then what would be the use case here?