ApplyAbiChangeToKotlinSourceFileMutator doesn't put separator

[HaliksaR]

ApplyAbiChangeToKotlinSourceFileMutator doesn't put separator.

Because of this, the assembly crashes when modified via apply-abi-change-to in the file with the data class.

[asodja]

Looks like a bug, yes.

I believe the problem shows only for classes without a body, e.g.:

data class Thing(
    val property: String = "thing"
) : Serializable