README.md in avro-builder-0.3.0 vs README.md in avro-builder-0.3.1

@@ -106,20 +106,22 @@
     {
       "name": "full_name",
       "type": [
         "null",
         "string"
-      ]
+      ],
+      "default": null
     }
   ]
 }
 ```
 
 ### Required and Optional
 
 Fields for a record are specified as `required` or `optional`. Optional fields are
-implemented as a union in Avro, where `null` is the first type in the union.
+implemented as a union in Avro, where `null` is the first type in the union and
+the field has a default value of `null`.
 
 ### Named Types
 
 `fixed` and `enum` fields may be specified inline as part of a record
 or as standalone named types.
@@ -204,10 +206,10 @@
   optional :opt_union, :union, types: [:float, :long]
 end
 ```
 
 For an optional union, `null` is automatically added as the first type for
-the union.
+the union and the field defaults to `null`.
 
 ### Auto-loading and Imports
 
 Specify paths to search for definitions: