fix: Null example values generated for enum properties (#18623)

* Fix null example values being generated for enum properties

* Update examples

* PRFB: use isEnumSchema

modules/openapi-generator/src/main/java/org/openapitools/codegen/examples/ExampleGenerator.java

@@ -377,7 +377,7 @@ public class ExampleGenerator {
                 return null;
             }
             return resolvePropertyToExample(name, mediaType, found.get(), processedModels);
-        } else if (ModelUtils.isArraySchema(schema)) {
+        } else if (ModelUtils.isArraySchema(schema) || ModelUtils.isEnumSchema(schema)) {
             return resolvePropertyToExample(schema.getName(), mediaType, schema, processedModels);
         } else {
             // TODO log an error message as the model does not have any properties

modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java

@@ -20,7 +20,6 @@ package org.openapitools.codegen.utils;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import io.swagger.v3.core.util.AnnotationsUtils;
-import io.swagger.v3.core.util.Json;
 import io.swagger.v3.oas.models.OpenAPI;
 import io.swagger.v3.oas.models.Operation;
 import io.swagger.v3.oas.models.PathItem;

modules/openapi-generator/src/test/java/org/openapitools/codegen/yaml/YamlGeneratorTest.java

@@ -28,6 +28,7 @@ import org.testng.annotations.Test;
 
 import java.io.File;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -121,4 +122,31 @@ public class YamlGeneratorTest {
         Assert.assertEquals(actual.getPaths().get("/foo/bar").getPost().getResponses().get("200").getContent().get("*/*").getSchema().getAdditionalProperties(),
                 expected.getComponents().getSchemas().get("_foo_bar_post_200_response").getAdditionalProperties());
     }
+
+    @Test
+    public void testIssue18622() throws Exception {
+        Map<String, Object> properties = new HashMap<>();
+        properties.put(OpenAPIYamlGenerator.OUTPUT_NAME, "issue_18622.yaml");
+
+        File output = Files.createTempDirectory("issue_18622").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("openapi-yaml")
+                .setAdditionalProperties(properties)
+                .setInputSpec("src/test/resources/2_0/issue_18622.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        final ClientOptInput clientOptInput = configurator.toClientOptInput();
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(clientOptInput).generate();
+        Assert.assertEquals(files.size(), 5);
+        TestUtils.ensureContainsFile(files, output, "issue_18622.yaml");
+
+        OpenAPI expected = TestUtils.parseSpec("src/test/resources/2_0/issue_18622_expected.yaml");
+        OpenAPI actual = TestUtils.parseSpec(Path.of(output.getAbsolutePath(), "issue_18622.yaml").toString());
+
+        Assert.assertEquals(actual.getComponents().getSchemas().get("myresponse").getExample(),
+                expected.getComponents().getSchemas().get("myresponse").getExample());
+    }
 }

modules/openapi-generator/src/test/resources/2_0/issue_18622.yaml

@@ -0,0 +1,27 @@
+swagger: '2.0'
+info:
+  title: 'Buggy Api'
+  version: '1.0'
+consumes:
+  - application/json
+paths:
+  /foo/bar:
+    post:
+      responses:
+        '200':
+          description: ok
+          schema:
+            $ref: "#/definitions/myresponse"
+definitions:
+  myresponse:
+    type: object
+    additionalProperties: false
+    properties:
+      x:
+        $ref: "#/definitions/myenum"
+  myenum:
+    type: string
+    enum:
+      - A
+      - B
+      - C

modules/openapi-generator/src/test/resources/2_0/issue_18622_expected.yaml

@@ -0,0 +1,33 @@
+openapi: 3.0.1
+info:
+  title: Buggy Api
+  version: "1.0"
+servers:
+  - url: /
+paths:
+  /foo/bar:
+    post:
+      responses:
+        "200":
+          content:
+            '*/*':
+              schema:
+                $ref: '#/components/schemas/myresponse'
+          description: ok
+components:
+  schemas:
+    myresponse:
+      additionalProperties: false
+      example:
+        x: A
+      properties:
+        x:
+          $ref: '#/components/schemas/myenum'
+      type: object
+    myenum:
+      enum:
+        - A
+        - B
+        - C
+      type: string
+x-original-swagger-version: "2.0"

samples/client/petstore/csharp/generichost/net8/FormModels/api/openapi.yaml

@@ -1276,7 +1276,7 @@ components:
         id: 0
         shipDate: 2020-02-02T20:20:20.000222Z
         complete: false
-        status: null
+        status: placed
       properties:
         id:
           format: int64
@@ -1400,7 +1400,7 @@ components:
           id: 1
         - name: name
           id: 1
-        status: null
+        status: available
       properties:
         id:
           format: int64