Support nullable org.springframework.web.multipart.MultipartFile in Kotlin Spring generator

- nullable is only supported for MultipartFile. However, Array<MultipartFile> could be also nullable

Author: jreynard-code

modules/openapi-generator/src/main/resources/kotlin-spring/optionalDataType.mustache

@@ -1 +1 @@
-{{^isFile}}{{{dataType}}}{{^required}}{{^defaultValue}}?{{/defaultValue}}{{/required}}{{/isFile}}{{#isFile}}{{#isArray}}Array<{{/isArray}}org.springframework.web.multipart.MultipartFile{{#isArray}}>{{/isArray}}{{^isArray}}{{^required}}?{{/required}}{{/isArray}}{{/isFile}}
+{{^isFile}}{{{dataType}}}{{^required}}{{^defaultValue}}?{{/defaultValue}}{{/required}}{{/isFile}}{{#isFile}}{{#isArray}}Array<{{/isArray}}org.springframework.web.multipart.MultipartFile{{#isArray}}>{{/isArray}}{{^required}}?{{/required}}{{/isFile}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java

@@ -370,6 +370,40 @@ public void delegateReactiveWithTags() throws Exception {
                 "ApiUtil");
     }
 
+
+    @Test
+    public void testNullableMultipartFile() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+
+        OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_0/kotlin/feat-multipartfile_nullable.yaml", null, new ParseOptions()).getOpenAPI();
+
+        KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(CXFServerFeatures.LOAD_TEST_DATA_FROM_FILE, "true");
+
+        ClientOptInput input = new ClientOptInput();
+        input.openAPI(openAPI);
+        input.config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+
+        generator.opts(input).generate();
+
+        assertFileContains(Paths.get(outputPath + "/src/main/kotlin/org/openapitools/api/NullableMultipartfileApiController.kt"),
+                "file: org.springframework.web.multipart.MultipartFile?");
+        assertFileContains(Paths.get(outputPath + "/src/main/kotlin/org/openapitools/api/NullableMultipartfileArrayApiController.kt"),
+                "files: Array<org.springframework.web.multipart.MultipartFile>?");
+    }
+
     @Test
     public void arrayItemsCanBeNullable() throws IOException {
         File output = Files.createTempDirectory("test").toFile().getCanonicalFile();

modules/openapi-generator/src/test/resources/3_0/kotlin/feat-multipartfile_nullable.yaml

@@ -0,0 +1,109 @@
+openapi: 3.0.0
+servers:
+  - url: 'https://example.org/v1'
+info:
+  description: >-
+    Example created for nullable multipartfile issue
+  version: 1.0.0
+  title: OpenAPI Stuff API created to reproduce issue
+  license:
+    name: Apache-2.0
+    url: 'https://www.apache.org/licenses/LICENSE-2.0.html'
+tags:
+  - name: multipartfile
+    description: All about the nullable multipartfile
+security:
+  - bearerAuth: []
+paths:
+  /nullable-multipartfile:
+    post:
+      tags:
+        - multipartfile
+      summary: simple nullable multipartfile
+      operationId: testNullableMultipartfile
+      requestBody:
+        content:
+          multipart/form-data:
+            schema:
+              type: object
+              properties:
+                file:
+                  type: string
+                  description: File to upload
+                  format: binary
+                jsonPayload:
+                  type: object
+                  description: simple json payload
+                  properties:
+                    name:
+                      type: string
+              required:
+                - jsonPayload
+      responses:
+        '200':
+          description: successful operation
+          content:
+            application/json:
+              schema:
+                type: string
+        '400':
+          description: Invalid status value
+
+  /nullable-multipartfile-array:
+    post:
+      tags:
+        - multipartfile
+      summary: simple nullable multipartfile
+      operationId: testNullableMultipartfile
+      requestBody:
+        content:
+          multipart/form-data:
+            schema:
+              type: object
+              properties:
+                files:
+                  type: array
+                  items:
+                    type: string
+                    description: File to upload
+                    format: binary
+                jsonPayload:
+                  type: object
+                  description: simple json payload
+                  properties:
+                    name:
+                      type: string
+              required:
+                - jsonPayload
+      responses:
+        '200':
+          description: successful operation
+          content:
+            application/json:
+              schema:
+                type: string
+        '400':
+          description: Invalid status value
+externalDocs:
+  description: Find out more about Swagger
+  url: 'http://swagger.io'
+components:
+  securitySchemes:
+    bearerAuth:
+      type: http
+      scheme: bearer
+      bearerFormat: JWT
+  schemas:
+    Stuff:
+      type: object
+      properties:
+        id:
+          type: integer
+          format: int64
+        name:
+          type: string
+        tag:
+          type: string
+      required:
+        - name
+