Passing nullable parameters to a Page via PageParameters in Wicket 6

Question

I need to pass a parameter to my page and I can't find a way to pass parameters that might be null.

If I do:

PageParameters pageParameters = new PageParameters ();
pageParameters.add ("key", null);

This will result in an exception

java.lang.IllegalArgumentException: Argument 'value' may not be null. at org.apache.wicket.util.lang.Args.notNull(Args.java:41)

If I use Google Guava's Optional, I can't find any way to cast the object even if the the Optional object is not holding a null ie not equals to Optional.absent() :

In my landing page's constructor I do

StringValue sv = parameters.get ("key");
sv.to ( Optional.of (MyEnum.SOME_ENUM_CONSTANT).getClass () );

and when I run it I get this error:

org.apache.wicket.util.string.StringValueConversionException: Cannot convert 'Optional.of(SOME_ENUM_CONSTANT)'to type class com.google.common.base.Present.

Am I doing something wrong?

Is there any other way to pass a possibly null object in wicket 6?

I noticed in wicket 1.4 they have PageParameters.NULL which seems to have dissapeared in wicket 6.

Thank you

Answer 1

This might be too simple, but what's wrong with

Object value = ?
if (value != null) {
    pageParameters.add ("key", value);
}

and

StringValue sv = pageParameters.get("key");
if (!sv.isNull()) {
    // process string value
}

Answer 2

All page parameters in wicket will be treated as Strings eventually. The idea is that a page parameter will be on the URL of the request.

From the javadoc:

Suppose we mounted a page on /user and the following url was accessed /user/profile/bob?action=view&redirect=false. In this example profile and bob are indexed parameters with respective indexes 0 and 1. action and redirect are named parameters.

If you add something like x=y&x, the parameter x will appear twice, once with the String y and another with the empty string.

Depending on what you are trying to accomplish I would suggest to either

• Don't pass the parameter at all when there is a null value required and use the isNull or toOptional methods.
• Use indexed parameters and test for presence of a certain word