code: public void setUsernameAttributes(java.util.Collection<String> usernameAttributes) {
          if (usernameAttributes == null) {
              this.usernameAttributes = null;
              return;
          }
  
          this.usernameAttributes = new java.util.ArrayList<String>(usernameAttributes);
      }
docs: <p>
  Specifies whether email addresses or phone numbers can be specified as usernames when a user signs up.
  </p>
  
  @param usernameAttributes
  Specifies whether email addresses or phone numbers can be specified as usernames when a user signs up.
  @see UsernameAttributeType