Simple fix for serializing button inputs. Devices that do not have button inputs should not have this field at all.
Button input mode is simplified in new ds model, and has 3 options: disabled, 1way or 2way. The specific options and their mapping to old model values are based on Michael Tross explanation, but so far there is no solid document with this mapping to my knowledge. Only partial information can be found in https://intranet.aizo.net/_layouts/15/start.aspx#/Wiki/Parametersatz.aspx (bank3, address: 0x1e), and (outdated) ds-basics.pdf.