Why this problem occurs?

NullReferenceException
Object reference not set to an instance of an object
UIDrawCall.set_isDirty (Boolean value)
UnityEngine.Transform.TransformPoint (Vector3 position)
UIPanel.UpdateDrawCalls ()
UIPanel.LateUpdate ()
06-25 07:10:12.388 17810 17848 I Unity : NullReferenceException: Object reference not set to an instance of an object
06-25 07:10:12.388 17810 17848 I Unity : at UIDrawCall.set_isDirty (Boolean value) [0x00000] in <filename unknown>:0
06-25 07:10:12.388 17810 17848 I Unity : at UnityEngine.Transform.TransformPoint (Vector3 position) [0x00000] in <filename unknown>:0
06-25 07:10:12.388 17810 17848 I Unity : at UIPanel.UpdateDrawCalls () [0x00000] in <filename unknown>:0
06-25 07:10:12.388 17810 17848 I Unity : at UIPanel.LateUpdate () [0x00000] in <filename unknown>:0
How to solve this problem? Thanks!~