Currently the generated bindings assume that any object
passed to Go as a method argument is actually a valid one
originating from Go. The `null` object is however a corner
case to this assumption, which should be accepted for Go
pointer types, since they can cleanly convert into `nil`.
This CL modifies the generated wrapper code so any `nil`
reference is permitted for Go pointer types, which until
now produced a nil pointer dereference error.
Fixesgolang/go#20330
Change-Id: If1ab9cf9df7ac3808486d23ccf2db8d32fb89426
Reviewed-on: https://go-review.googlesource.com/43253
Reviewed-by: Elias Naur <elias.naur@gmail.com>