IsZero() panics with nil *strfmt.DateTime

[amadorcervera]

I have a swagger specification with an object that has an optional string property with date-time format. The code generated for this field is:

NotAfter *strfmt.DateTime `json:"not_after,omitempty"`

and the validation function generated:

func (m *SigningProfile) validateNotAfter(formats strfmt.Registry) error {
	if swag.IsZero(m.NotAfter) { // not required
		return nil
	}

	if err := validate.FormatOf("not_after", "body", "date-time", m.NotAfter.String(), formats); err != nil {
		return err
	}

	return nil
}

When this field is not set, that is when is nil, the call to swag.IsZero() panics:

panic: value method github.com/go-openapi/strfmt.DateTime.IsZero called using nil *DateTime pointer

My code hasn't been modified in months and it was working perfectly few days ago. I think the problem could be related with the changes from this commit in strfmt: Adds IsZero functionality to DateTime and the beginning of the IsZero() function:

func IsZero(data interface{}) bool {
	// check for things that have an IsZero method instead
	if vv, ok := data.(zeroable); ok {
		return vv.IsZero()
	}

because now strfmt.DateTime is zeroable. Previously should go through this case in the switch:

	case reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
		return v.IsNil()