I have a driver and a number of the inputs are set with required:false. When i do not populate a value with the latest hub firmware (220.127.116.11) I cannot save the preferences. On 2.3.4 I am sure this was possible. So to me this looks like a bug.
input name: 'assocGroup2', type: 'text', required: false, title: 'Association group 2: '