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

Update kotlin-spring-additionalproperties samples

Author: jreynard-code

samples/server/petstore/kotlin-springboot-additionalproperties/src/main/kotlin/org/openapitools/api/PetApiController.kt

@@ -106,7 +106,7 @@ class PetApiController(@Autowired(required = true) val service: PetApiService) {
         produces = ["application/json"],
         consumes = ["multipart/form-data"]
     )
-    fun uploadFile( @PathVariable("petId") petId: kotlin.Long, @Valid @RequestParam(value = "additionalMetadata", required = false) additionalMetadata: kotlin.String? , @Valid @RequestPart("file", required = false) file: org.springframework.web.multipart.MultipartFile?): ResponseEntity<ModelApiResponse> {
+    fun uploadFile( @PathVariable("petId") petId: kotlin.Long, @Valid @RequestParam(value = "additionalMetadata", required = false) additionalMetadata: kotlin.String? , @Valid @RequestPart("file", required = false) file: org.springframework.web.multipart.MultipartFile): ResponseEntity<ModelApiResponse> {
         return ResponseEntity(service.uploadFile(petId, additionalMetadata, file), HttpStatus.valueOf(200))
     }
 }

samples/server/petstore/kotlin-springboot-additionalproperties/src/main/kotlin/org/openapitools/api/PetApiService.kt

@@ -99,5 +99,5 @@ interface PetApiService {
      * @return successful operation (status code 200)
      * @see PetApi#uploadFile
      */
-    fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: org.springframework.web.multipart.MultipartFile?): ModelApiResponse
+    fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: org.springframework.web.multipart.MultipartFile): ModelApiResponse
 }

samples/server/petstore/kotlin-springboot-additionalproperties/src/main/kotlin/org/openapitools/api/PetApiServiceImpl.kt

@@ -34,7 +34,7 @@ class PetApiServiceImpl : PetApiService {
         TODO("Implement me")
     }
 
-    override fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: org.springframework.web.multipart.MultipartFile?): ModelApiResponse {
+    override fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: org.springframework.web.multipart.MultipartFile): ModelApiResponse {
         TODO("Implement me")
     }
 }