class Vips::Object

def get_pspec name

which you must clear
return a pspec, or nil ... nil wil leave a message in the error log 
def get_pspec name
  ppspec = GObject::GParamSpecPtr.new
  argument_class = Vips::ArgumentClassPtr.new
  argument_instance = Vips::ArgumentInstancePtr.new
  result = Vips.vips_object_get_argument self, name,
    ppspec, argument_class, argument_instance
  return nil if result != 0
  ppspec[:value]
end