Merge pull request #9936 from swagger-api/ticket-7656

refs #7656 - fix random enum failure in csharp

Author: frantuma

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractCSharpCodegen.java

@@ -408,7 +408,7 @@ private void postProcessEnumRefs(final Map<String, Object> models) {
                         // This is different in C# than most other generators, because enums in C# are compiled to integral types,
                         // while enums in many other languages are true objects.
                         CodegenModel refModel = enumRefs.get(var.datatype);
-                        var.allowableValues = refModel.allowableValues;
+                        var.allowableValues = new HashMap<>(refModel.allowableValues);
                         var.isEnum = true;
 
                         updateCodegenPropertyEnum(var);