Add documentation for using null values in DB2i extensions

Signed-off-by: worksofliam <[email protected]>

Author: worksofliam

src/content/docs/extensions/db2i/index.mdx

@@ -70,6 +70,10 @@ A fully qualified table name is required for the fields to be editable.
 update: select * from sample.employee;
 ```
 
+#### Using nulls
+
+Enter the value `null` to set a column to *null*. If the column cannot accept at least 4 characters, then `-` (a dash) may be used.
+
 ## Syntax checking
 
 When connected to an IBM i, should be enabled. Here is what triggers to syntax checker: