fix #3071 - fixes empty enum in server variable

Author: frantuma

modules/swagger-core/src/main/java/io/swagger/v3/core/util/AnnotationsUtils.java

@@ -635,7 +635,9 @@ public static Optional<Server> getServer(io.swagger.v3.oas.annotations.servers.S
                 serverVariableObject.setDefault(serverVariable.defaultValue());
             }
             if (serverVariable.allowableValues() != null && serverVariable.allowableValues().length > 0) {
-                serverVariableObject.setEnum(Arrays.asList(serverVariable.allowableValues()));
+                if (StringUtils.isNotBlank(serverVariable.allowableValues()[0])) {
+                    serverVariableObject.setEnum(Arrays.asList(serverVariable.allowableValues()));
+                }
             }
             if (serverVariable.extensions() != null && serverVariable.extensions().length > 0) {
                 Map<String, Object> extensions = AnnotationsUtils.getExtensions(serverVariable.extensions());

modules/swagger-jaxrs2/src/test/java/io/swagger/v3/jaxrs2/annotations/definition/OpenApiDefinitionTest.java

@@ -15,6 +15,7 @@
 import java.io.IOException;
 
 public class OpenApiDefinitionTest extends AbstractAnnotationTest {
+
     @Test
     public void testSimpleInfoGet() throws IOException {
 
@@ -104,4 +105,44 @@ public void foo() {
 
     }
 
+    @Test
+    public void testServerVariableWithoutEnum() throws IOException {
+
+        String expectedYAML = "openapi: 3.0.1\n" +
+                "info:\n" +
+                "  title: My Rest API\n" +
+                "  description: My RESTful API implementation\n" +
+                "  version: 1.0.0\n" +
+                "servers:\n" +
+                "- url: /{context-path}/{rest-api}\n" +
+                "  description: My REST API\n" +
+                "  variables:\n" +
+                "    context-path:\n" +
+                "      default: my-war\n" +
+                "    rest-api:\n" +
+                "      enum:\n" +
+                "      - api\n" +
+                "      - rest\n" +
+                "      - batchapi\n" +
+                "      default: api\n";
+
+        compareAsYaml(OpenApiDefinitionTest.ServerVariableWithoutEnum.class, expectedYAML);
+    }
+
+    @OpenAPIDefinition(
+            info = @Info( title = "My Rest API", version = "1.0.0", description = "My RESTful API implementation" ),
+            servers = {
+                    @Server( description = "My REST API",
+                            url = "/{context-path}/{rest-api}",
+                            variables = {
+                            @ServerVariable(name = "context-path", defaultValue = "my-war"),
+                                    @ServerVariable(name = "rest-api", defaultValue = "api",
+                                            allowableValues = {"api", "rest", "batchapi"}) } ) } )
+    static class ServerVariableWithoutEnum {
+
+        public void foo() {
+        }
+
+    }
+
 }

modules/swagger-jaxrs2/src/test/java/io/swagger/v3/jaxrs2/resources/extensions/ExtensionsResource.java

@@ -387,8 +387,6 @@ public ExtensionUser setUser(
                     "servers:\n" +
                     "- variables:\n" +
                     "    aa:\n" +
-                    "      enum:\n" +
-                    "      - \"\"\n" +
                     "      default: aa\n" +
                     "      x-servervar:\n" +
                     "        name: Josh\n" +