[html-formfu] Password fields that do not update unless filled in

[Steve]

Hi,

I've got a form editing a user's username, email and password. As usual
the password fields are blank, and I don't want to update the password
field in the database unless the user indicates they want to change it
by filling it in.

Anyway, I can't figure out how to do this.

Relevant bit of application is pretty much part 9 of the Catalyst
tutorial. Here's the form config:

---
indicator: submit
elements:
    - type: Text
      name: username
      label: Username
      constraints:
        - Required
    - type: Text
      name: email
      label: Email
      constraints:
        - Required
    - type: Password
      name: password
      label: Password
      constraints:
        - type: Equal
          others: repeat_password
    - type: Password
      name: repeat_password
      label: Repeat Password
    - type: Submit
      name: submit
      value: Submit

Cheers,
Steve.