How do i get depth of field from volume?

if i use .TryGet that the error is: " **The type 'DepthOfField' cannot be used as type parameter 'T' in the generic type or method 'VolumeProfile.TryGet(out T)'. There is no implicit reference conversion from 'DepthOfField' to 'UnityEngine.Rendering.VolumeComponent'. **" It worked before fine, than something happened but something happened and i always get this error message