public static void propagate (out Error? dest, owned Error src)
dest is null, free
src; otherwise, moves
src into *
The error variable
dest points to must be null.
src must be non-null.
src is no longer valid after this call. If you want to keep using the same GError*, you need to set it to
null after calling this function on it.
error return location
error to move into the return location