In the Declarative Directive Generator for a Multibranch Pipeline project, I am able to add a string parameter and generate the directive:

parameters {
  string defaultValue: '', description: '', name: 'demo1', trim: false
}

However, when I try to add a second string parameter, by first clicking "Add" and then clicking "string: String parameter" in the dropdown list, nothing happens. It seems the Declarative Directive Generator allows at most one parameter of each type. AFAIK, the parameters directive itself allows multiple parameters of the same type, so the Declarative Directive Generator should likewise allow them.