fix: guard putAdditionalProperty in setter against models without additionalProperties

Generating the putAdditionalProperty call when additionalProperties is false
would cause a compile error because putAdditionalProperty is only generated
for models that have an additionalProperties schema.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: charlie-zhang109

.generator/src/generator/templates/modelSimple.j2

@@ -258,7 +258,7 @@ public class {{ name }} {%- if model.get("x-generate-alias-as-model") %} extends
     {%- else %}
     this.{{ variableName }} = {{ variableName }};
     {%- endif %}
-    {%- if model.get("x-keep-typed-in-additional-properties") %}
+    {%- if model.get("x-keep-typed-in-additional-properties") and model.additionalProperties is not false %}
     putAdditionalProperty(JSON_PROPERTY_{{ attr|snake_case|upper }}, {%- if not isRequired and isNullable %} this.{{ variableName }}.orElse(null){%- else %} {{ variableName }}{%- endif %});
     {%- endif %}
   }