NullReferenceException

[SiMaLaoShi]

NullReferenceException: Object reference not set to an instance of an object
WaterSystem.Data.WaterSurfaceDataEditor.OnInspectorGUI () (at Packages/com.verasl.water-system/Editor/WaterSurfaceDataEditor.cs:230)
WaterSystem.WaterEditor.OnInspectorGUI () (at Packages/com.verasl.water-system/Editor/WaterEditor.cs:29)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass59_0.b__0 () (at :0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)