[Kotlin] Primitive array items validity check (OpenAPITools#21315)

* Primitive array items validity check

* Update samples

Author: andreas-umbricht

modules/openapi-generator/src/main/resources/kotlin-client/data_class.mustache

@@ -291,6 +291,16 @@ import {{packageName}}.infrastructure.ITransformForStorage
               String.format("Expected the field `{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}` to be an array in the JSON string but got `%s`", jsonObj["{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}"].toString())
             }
             {{/required}}
+            {{#items.isPrimitiveType}}
+            // ensure the items in json array are primitive
+            if (jsonObj["{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}"] != null) {
+              for (i in 0 until jsonObj.getAsJsonArray("{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}").size()) {
+                require(jsonObj.getAsJsonArray("{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}").get(i).isJsonPrimitive) {
+                  String.format("Expected the property in array `{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}` to be primitive")
+                }
+              }
+            }
+            {{/items.isPrimitiveType}}
             {{/items.isModel}}
             {{/isArray}}
             {{^isContainer}}

samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiPet.kt

@@ -151,6 +151,14 @@ data class ApiPet (
             require(jsonObj["photoUrls"].isJsonArray()) {
               String.format("Expected the field `photoUrls` to be an array in the JSON string but got `%s`", jsonObj["photoUrls"].toString())
             }
+            // ensure the items in json array are primitive
+            if (jsonObj["photoUrls"] != null) {
+              for (i in 0 until jsonObj.getAsJsonArray("photoUrls").size()) {
+                require(jsonObj.getAsJsonArray("photoUrls").get(i).isJsonPrimitive) {
+                  String.format("Expected the property in array `photoUrls` to be primitive")
+                }
+              }
+            }
             // validate the optional field `category`
             if (jsonObj["category"] != null && !jsonObj["category"].isJsonNull) {
               ApiCategory.validateJsonElement(jsonObj["category"])