MOD-7009: Search and Query - Empty indexing (#199)

* Initial docs for empty indexing

* Renaming empty indexing

---------

Co-authored-by: David Dougherty <david.dougherty@redis.com>

content/commands/ft.create/index.md

@@ -118,6 +118,10 @@ arguments:
     optional: true
     token: WITHSUFFIXTRIE
     type: pure-token
+  - name: indexempty
+    optional: true
+    token: INDEXEMPTY
+    type: pure-token
   - arguments:
     - name: sortable
       token: SORTABLE
@@ -259,7 +263,10 @@ after the SCHEMA keyword, declares which fields to index:
 
   - `WITHSUFFIXTRIE` for `TEXT` and `TAG` attributes, keeps a suffix trie with all terms which match the suffix. It is used to optimize `contains` (*foo*) and `suffix` (*foo) queries. Otherwise, a brute-force search on the trie is performed. If suffix trie exists for some fields, these queries will be disabled for other fields.
 
+  - `INDEXEMPTY` for `TEXT` and `TAG` attributes, allows you to index and search for empty strings. By default, empty strings are not indexed.
+
   - `INDEXMISSING` for all field types, allows you to search for missing values, that is, documents that do not contain a specific field. Note the difference between a field with an empty value and a document with a missing value. By default, missing values are not indexed.
+
 </details>
 
 ## Optional arguments

content/develop/interact/search-and-query/query/combined.md

@@ -145,11 +145,3 @@ FT.SEARCH idx:bikes_vss "(@price:[500 1000] @condition:{new})=>[KNN 3 @vector $q
 ```
 
 The [vector search article]({{< relref "/develop/interact/search-and-query/query/vector-search" >}}) provides further details about vector queries in general.
-
-## Missing values
-
-You can use the `ismissing(@field)` query function to search for documents that do not contain a specific field (provided this field indexes missing values).
-
-```
-FT.SEARCH idx:bikes "ismissing(@price) @description:(kids | small)"
-```