UnityEditor.SerializedProperty' does not contain a definition for `GetArrayItems'

I am trying to upgrade my vuforia project to latest vuforia 6.2 i followed instructions adding configurationupgrade.cs inside editor but getting this error need help please.

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Assets/ConfigurationUpgrade.cs(321,60): error CS1061: Type UnityEditor.SerializedProperty' does not contain a definition for GetArrayItems' and no extension method GetArrayItems' of type UnityEditor.SerializedProperty' could be found. Are you missing an assembly reference?

Blockquote

Code line : serializedObject.FindProperty(property.BehaviourName).GetArrayItems(out data);