Unity Serializedobject of serializedproperty has been disposed hatası veriyor

Nullreferenceexception: Serializedobject of serializedproperty has been disposed.
Unityeditor. Serializedproperty. Get_boolvalue () (at <1885898B95CC400580FF334D9D2F9C0f>:0)
Unityeditor. Modelımportermaterialeditor. Domaterialsguı () (at <1885898B95CC400580FF334D9D2F9C0f>:0)
Unityeditor. Modelımportermaterialeditor. Onınspectorguı () (at <1885898B95CC400580FF334D9D2F9C0f>:0)
Unityeditor. Assetımportertabbededitor. Onınspectorguı () (at <1885898B95CC400580FF334D9D2F9C0f>:0)
Unityeditor. Modelımportereditor. Onınspectorguı () (at <1885898B95CC400580FF334D9D2F9C0f>:0)
Unityeditor. Uıelements. Inspectorelement+<>c__displayclass72_0.<createınspectorelementusingımguı>b__0 () (at <1885898B95CC400580FF334D9D2F9C0f>:0)
Unityengine. Guıutility: Processevent(ınt32, ıntptr, boolean&)

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