Added missing docs for ignore-null-fields for JSON

docs/import/import-files/json.md

@@ -117,6 +117,39 @@ can help with indexing purposes in MarkLogic as well. To include a JSON root fie
 use the `--json-root-name` option with a value for the name of the root field. The data read from a 
 row will then be nested under this root field.
 
+## Ignoring null fields
+
+By default, Flux will include any fields in a JSON Lines file that have a null value (this does not include
+a value that has whitespace) when creating JSON or XML documents. You can instead ignore fields with a null value
+via the `--ignore-null-fields` option:
+
+{% tabs log %}
+{% tab log Unix %}
+```
+./bin/flux import-aggregate-json-files \
+    --json-lines \
+    --path path/to/file.txt \
+    --connection-string "flux-example-user:password@localhost:8004" \
+    --permissions flux-example-role,read,flux-example-role,update \
+    --ignore-null-fields
+```
+{% endtab %}
+{% tab log Windows %}
+```
+bin\flux import-aggregate-json-files ^
+    --json-lines ^
+    --path path\to\file.txt ^
+    --connection-string "flux-example-user:password@localhost:8004" ^
+    --permissions flux-example-role,read,flux-example-role,update ^
+    --ignore-null-fields
+```
+{% endtab %}
+{% endtabs %}
+
+The decision on whether to include null fields will depend on your application requirements. For example, if your
+documents have large numbers of null fields, you may find them to be noise and decide to ignore them. In another case,
+it may be important to query for documents that have a particular field with a value of null.
+
 ## Specifying an encoding
 
 MarkLogic stores all content [in the UTF-8 encoding](https://docs.marklogic.com/guide/search-dev/encodings_collations#id_87576).