fallback to just map

Author: ChiragAgg5k

templates/dart/lib/src/models/model.dart.twig

@@ -47,7 +47,7 @@ class {{ definition.name | caseUcfirst | overrideIdentifier }} implements Model
             {%- endif -%},
 {% endfor %}
 {% if definition.additionalProperties %}
-            data: map["data"],
+            data: map["data"] ?? map,
 {% endif %}
         );
     }