Just set that field as Mandatory.
I have marked the field as mandatory and still i see <None> in the request form.
I've got the same problem in 7.6 still
I've tried setting the field to "Required" = "Yes" but it makes no difference. I've used the Chrome Developer tools to drill down into the page content and the <None> option is always inserted into the page. My underlying External action returns a String array loaded from a ConfigurationElement in vRO so this is being added to the page by the server or the page renderer.
Does anyone have a suggestion or solution? This is going to confuse users as the <None> option can be selected and submitted even though I don't want it to be permitted