documents.yaml

_id: 1
foo: null
bar: null
---
_id: 2
foo: ''
bar: ''
---
_id: 3
foo: bar
bar: baz

mappings.yaml

type:
    properties: 
        foo: 
            type: string
            index: not_analyzed
            
        

play.sh

#!/bin/bash

export ELASTICSEARCH_ENDPOINT="http://localhost:9200"

# Create indexes

curl -XPUT "$ELASTICSEARCH_ENDPOINT/play" -d '{
    "settings": {},
    "mappings": {
        "type": {
            "properties": {
                "foo": {
                    "type": "string",
                    "index": "not_analyzed"
                }
            }
        }
    }
}'


# Index documents
curl -XPOST "$ELASTICSEARCH_ENDPOINT/_bulk?refresh=true" -d '
{"index":{"_index":"play","_type":"type","_id":1}}
{"foo":null,"bar":null}
{"index":{"_index":"play","_type":"type","_id":2}}
{"foo":"","bar":""}
{"index":{"_index":"play","_type":"type","_id":3}}
{"foo":"bar","bar":"baz"}
'

# Do searches

curl -XPOST "$ELASTICSEARCH_ENDPOINT/_search?pretty" -d '
{
    "query": {
        "filtered": {
            "filter": {
                "term": {
                    "foo": ""
                }
            }
        }
    }
}
'

curl -XPOST "$ELASTICSEARCH_ENDPOINT/_search?pretty" -d '
{
    "query": {
        "filtered": {
            "filter": {
                "missing": {
                    "field": "bar"
                }
            }
        }
    }
}
'

play.yaml

# Auto generated by Found's Play-tool at 2013-12-12T13:22:01+01:00
version: 0
title: empty strings vs. analysis/missing
description: ""

searches.yaml

# This will match only the 2nd document. Note that the "foo"-field is not_analyzed
query: 
    filtered: 
        filter: 
            term: 
                foo: ''
---
# This will match both 1 and 2. For an analyzed field, there is no difference between a missing field and an empty string.
query: 
    filtered: 
        filter: 
            missing: 
                field: bar