修复对当ReturnParameterType是EnumModelType的支持

Map/MethodMap.cs

@@ -117,6 +117,11 @@ namespace FlutterCodeGenerator.Map
                     dartString.AppendLine($"\t\tvar result = (rpcRst as Map).cast<{dictionaryModelType.GenericArgumentModelTypeList[0].GetFlutterTypeName()},{dictionaryModelType.GenericArgumentModelTypeList[1].GetFlutterTypeName()}>();");
                     dartString.AppendLine("\t\treturn result;");
                 }
+                else if (ReturnParameterModelType is EnumModelType enumModelType)
+                {
+                    dartString.AppendLine($"\t\tvar result = {enumModelType.GetFlutterTypeName()}.values.firstWhere((e) => e.index == rpcRst);");
+                    dartString.AppendLine("\t\treturn result;");
+                }
             }
             dartString.AppendLine("\t}");
             return dartString.ToString();