Is this a bug?? (Unable to find style 'my enum type' in skin 'DarkSkin' Layout)

hello there

i am trying to popup enum in window editor when i open the window i got this Warning

Unable to find style 'here my enum type name' in skin 'DarkSkin' Layout
UnityEngine.GUIStyle : op_Implicit(String)

and the enum field not show in the window editor and the enum 1st element show only in red color

i use this code with GUILayout.Window

Code (CSharp):

1. task = (TaskType)EditorGUILayout.EnumPopup(task, "Task Type");

i try it on unity2019.4.15.f1
and
unity2019.4.17.f1

both show the same issue

 

update

i used EditorStyles.popup and the enum popup showed up

Code (CSharp):

1.         GUILayout.Label("Task Type", EditorStyles.boldLabel);
2.         task = (TaskType)EditorGUILayout.EnumPopup(task, EditorStyles.popup);